JOSM sometimes not saving properly

[Roadsguy]

Not sure if this is where I should be posting this, but I couldn't find a better place.

I sometimes work on a custom .osm file made up of fictional fixes for various road situations (e.g. freeways where there aren't, rationalizing interchange setups, etc.) for fun, but sometimes it somehow doesn't save properly. I frequently do CTRL+S out of habit, but sometimes closing it and coming back to it later shows that a lot of what I had previously done did not save. This seems to be unpredictable. I'm not sure if leaving it open for a while affects it.

While what I'm doing may not be important to OSM at all, progress on anything not saving when it should is definitely a major issue.