download of relation members sometimes does not notice a (suspected) download error

[aceman]

I was using JOSM on a congested network connection. On many upload/download operations I got proper timeout error dialogs. I just retried the operation until it succeeded.

But I noticed one case where this seems to not work properly.
When opening a relation (in this case type=route of a bus) I clicked the button to download all missing members. Everything looked fine. Just that when the members of the relation got rendered on the editing area, I noticed the WAYS are missing (a bus route relation contains bus stops (usually nodes) and ways on which the bus operates (may be across whole city)). So many nodes along the bus route were rendered fine (pedestrian crossings and traffic signals that were members of the roads and ways). But the actual roads (ways) were not shown. I also enabled a layer that overlays a line to outline the bus route in the street network. In this layer, the route was wrong, not on the expected roads, but it went to the top left corner of the editing window. It appears to me as if the downloaded (or not) ways had coordinates of zero or undefined. JOSM didn't crash or something but I intermediately restarted it when this happened. This happened to me several times (in about 10% of cases).

So I suspect there is a path in this members download code where JOSM does not detect some objects were not properly downloaded. Can you please check it?

[Don-vip]

Replying to aceman:

Can you please check it?

With so little concrete information, no. Your problem looks like tricky and we will need a lot more info. If you manage to reproduce, please attach at least:

• Your full system info
• A session archive containing all your layers
• The complete console output for your entire session
• A screenshot

[aceman]

Ok, what is a "A session archive" ?

[Don-vip]

A .joz file (File -> Session -> Save session)

[Don-vip]

Did you manage to reproduce ?

[aceman]

Sorry, not yet. It is hard to reproduce the congested network scenario. I assume it has to do with running some torrent downloads and I do not do that often. But I have tried it and JOSM didn't fail yet (as I wrote there is only a small chance the error happens).

Are there many downloading codepaths in this member downloading feature that it is not so easy to look at all of them whether returned network errors are handled?

It appears to me from the flashing dialogs that JOSM downloads some "package of nodes" and "package of ways". It appears to me that the error symptoms look like the nodes (traffic signals, pedestrian crossings) are downloaded correctly, but the ways (roads) connecting them are not.