Update of FlatLaf PLugin fails

[Klumbumbus]

What steps will reproduce the problem?

1. start JOSM
2. Error message

A manual update in the preferences doesn't work either.

see also attached screenshots.

console from the beginning:

2020-10-10 11:10:18.599 INFORMATION: Protokollierungsgrad ist bei INFORMATION (INFO, 800)
2020-10-10 11:10:19.257 INFO: Detected useable IPv6 network, preferring IPv6 over IPv4.
2020-10-10 11:10:20.788 WARNING: Could not open/create prefs root node Software\JavaSoft\Prefs at root 0x80000002. Windows RegCreateKeyEx(...) returned error code 5.
2020-10-10 11:10:22.588 INFO: loading plugin 'flatlaf' (version 35568)
2020-10-10 11:10:24.617 INFO: Running plugin update after JOSM upgrade. Automatic update at startup is enabled.
2020-10-10 11:10:24.866 INFO: GET https://josm.openstreetmap.de/pluginicons?plugins=HouseNumberTaggingTool,OpeningHoursEditor,PicLayer,RoadSigns,SimplifyArea,apache-commons,buildings_tools,editgpx,ejml,flatlaf,geotools,imagery-xml-bounds,imagery_offset_db,javafx-windows,jaxb,jna,jogl,jts,log4j,measurement,photo_geotagging,photoadjust,pointInfo,reltoolbox,reverter,tageditor,tagging-preset-tester,terracer,turnlanes-tagging,turnrestrictions,undelete,utilsplugin2 -> HTTP/1.1 200 (211 ms)
2020-10-10 11:10:27.006 INFO: Downloading Plugin flatlaf...
2020-10-10 11:10:27.071 INFO: GET https://josm.openstreetmap.de/osmsvn/applications/editors/josm/dist/flatlaf.jar -> HTTP/1.1 200 (64 ms; 434 kB)
2020-10-10 11:10:27.075 SEVERE: org.openstreetmap.josm.plugins.PluginDownloadException: java.nio.file.FileSystemException: C:\Users\stefa\AppData\Roaming\JOSM\plugins\flatlaf.jar.new: Der Prozess kann nicht auf die Datei zugreifen, da sie von einem anderen Prozess verwendet wird.. Cause: java.nio.file.FileSystemException: C:\Users\stefa\AppData\Roaming\JOSM\plugins\flatlaf.jar.new: Der Prozess kann nicht auf die Datei zugreifen, da sie von einem anderen Prozess verwendet wird.
org.openstreetmap.josm.plugins.PluginDownloadException: java.nio.file.FileSystemException: C:\Users\stefa\AppData\Roaming\JOSM\plugins\flatlaf.jar.new: Der Prozess kann nicht auf die Datei zugreifen, da sie von einem anderen Prozess verwendet wird.

	at org.openstreetmap.josm.plugins.PluginDownloadTask.download(PluginDownloadTask.java:147)
	at org.openstreetmap.josm.plugins.PluginDownloadTask.realRun(PluginDownloadTask.java:175)
	at org.openstreetmap.josm.gui.PleaseWaitRunnable.doRealRun(PleaseWaitRunnable.java:94)
	at org.openstreetmap.josm.gui.PleaseWaitRunnable.run(PleaseWaitRunnable.java:142)
	at org.openstreetmap.josm.plugins.PluginHandler.updatePlugins(PluginHandler.java:1178)
	at org.openstreetmap.josm.gui.MainApplication.updateAndLoadEarlyPlugins(MainApplication.java:1141)
	at org.openstreetmap.josm.gui.MainApplication.mainJOSM(MainApplication.java:909)
	at org.openstreetmap.josm.gui.MainApplication$3.processArguments(MainApplication.java:277)
	at org.openstreetmap.josm.gui.MainApplication.main(MainApplication.java:714)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.lang.reflect.Method.invoke(Unknown Source)
	at com.sun.javaws.Launcher.executeApplication(Unknown Source)
	at com.sun.javaws.Launcher.executeMainClass(Unknown Source)
	at com.sun.javaws.Launcher.doLaunchApp(Unknown Source)
	at com.sun.javaws.Launcher.run(Unknown Source)
	at java.lang.Thread.run(Unknown Source)
Caused by: java.nio.file.FileSystemException: C:\Users\stefa\AppData\Roaming\JOSM\plugins\flatlaf.jar.new: Der Prozess kann nicht auf die Datei zugreifen, da sie von einem anderen Prozess verwendet wird.

	at sun.nio.fs.WindowsException.translateToIOException(Unknown Source)
	at sun.nio.fs.WindowsException.rethrowAsIOException(Unknown Source)
	at sun.nio.fs.WindowsException.rethrowAsIOException(Unknown Source)
	at sun.nio.fs.WindowsFileSystemProvider.implDelete(Unknown Source)
	at sun.nio.fs.AbstractFileSystemProvider.deleteIfExists(Unknown Source)
	at java.nio.file.Files.deleteIfExists(Unknown Source)
	at java.nio.file.Files.copy(Unknown Source)
	at org.openstreetmap.josm.plugins.PluginDownloadTask.download(PluginDownloadTask.java:131)
	... 17 more

2020-10-10 11:10:27.187 SEVERE: Plugin update failed - <html>Updating the following plugin has failed:<ul><li>flatlaf</li></ul>Please open the Preference Dialog after JOSM has started and try to update it manually.</html>
2020-10-10 11:10:54.264 WARNING: Failed to delete outdated plugin 'C:\Users\stefa\AppData\Roaming\JOSM\plugins\flatlaf.jar'.
2020-10-10 11:10:54.265 WARNING: Failed to install already downloaded plugin 'flatlaf'. Skipping installation. JOSM is still going to load the old plugin version.
2020-10-10 11:10:54.270 INFO: loading plugin 'jaxb' (version 35092)
2020-10-10 11:10:54.274 INFO: loading plugin 'javafx-windows' (version 35458)
2020-10-10 11:10:54.305 INFO: loading plugin 'log4j' (version 35092)

URL:https://josm.openstreetmap.de/svn/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2020-10-09 18:53:24 +0200 (Fri, 09 Oct 2020)
Build-Date:2020-10-10 01:30:48
Revision:17137
Relative:URL: ^/trunk

Identification: JOSM/1.5 (17137 en) Windows 10 64-Bit
OS Build number: Windows 10 Pro 1909 (18363)
Memory Usage: 790 MB / 1820 MB (372 MB allocated, but free)
Java version: 1.8.0_261-b12, Oracle Corporation, Java HotSpot(TM) 64-Bit Server VM
Look and Feel: com.sun.java.swing.plaf.windows.WindowsLookAndFeel
Screen: \Display0 1680x1050 (scaling 1.0x1.0)
Maximum Screen Size: 1680x1050
Best cursor sizes: 16x16 -> 32x32, 32x32 -> 32x32
VM arguments: [-Djava.security.manager, -Djava.security.policy=file:<java.home>\lib\security\javaws.policy, -DtrustProxy=true, -Djnlpx.home=<java.home>\bin, -Djnlpx.origFilenameArg=C:\Program Files (x86)\josm-latest.jnlp, -Djnlpx.remove=false, -Djava.util.Arrays.useLegacyMergeSort=true, -Djnlpx.heapsize=NULL,2048m, -Djnlpx.splashport=65017, -Djnlpx.jvm=<java.home>\bin\javaw.exe]

Plugins:
+ HouseNumberTaggingTool (35508)
+ OpeningHoursEditor (35414)
+ PicLayer (35405)
+ RoadSigns (35510)
+ SimplifyArea (35405)
+ apache-commons (35524)
+ buildings_tools (35570)
+ editgpx (35248)
+ ejml (35313)
+ flatlaf (35568)
+ geotools (35169)
+ imagery-xml-bounds (35546)
+ imagery_offset_db (35405)
+ javafx-windows (35458)
+ jaxb (35092)
+ jna (35092)
+ jogl (1.2.3)
+ jts (35122)
+ log4j (35092)
+ measurement (35405)
+ photo_geotagging (35499)
+ photoadjust (35405)
+ pointInfo (35565)
+ reltoolbox (35529)
+ reverter (35556)
+ tageditor (35258)
+ tagging-preset-tester (35267)
+ terracer (35560)
+ turnlanes-tagging (283)
+ turnrestrictions (35515)
+ undelete (35521)
+ utilsplugin2 (35487)

Tagging presets:
+ ...

Map paint styles:
+ ...

Validator rules:
+ ...

Last errors/warnings:
- 00008.487 E: org.openstreetmap.josm.plugins.PluginDownloadException: java.nio.file.FileSystemException: <josm.pref>\plugins\flatlaf.jar.new: Der Prozess kann nicht auf die Datei zugreifen, da sie von einem anderen Prozess verwendet wird.. Cause: java.nio.file.FileSystemException: <josm.pref>\plugins\flatlaf.jar.new: Der Prozess kann nicht auf die Datei zugreifen, da sie von einem anderen Prozess verwendet wird.
- 00008.598 E: Plugin update failed - <html>Updating the following plugin has failed:<ul><li>flatlaf</li></ul>Please open the Preference Dialog after JOSM has started and try to update it manually.</html>
- 00035.675 W: Failed to delete outdated plugin '<josm.pref>\plugins\flatlaf.jar'.
- 00035.676 W: Failed to install already downloaded plugin 'flatlaf'. Skipping installation. JOSM is still going to load the old plugin version.