And it's back. New model unfinished, but keep saving during build and reached 4107 bricks and unable to save... Stops on "uploadind data..." for about 15 minutes befor "Error: 0 error" shows up.

Got the same error again.
I suspect it is connected to the recurring "Bad Gateway"-error that keeps appearing.
Sometimes it helps to go for "Save As" in stead of just "Save", but not this time.

I'm using Firefox 84.0.2 (x64) with only 3-4 tabs.
This model has 8912 parts.

Here is a few screenshots showing the problem.

It is weird that it stops in the middle. Maybe it is related. I don't know. It looks like the server issue has been resolved. I didn't see the error at all in the past 2 days.

@Scrubs When you mention it I havent seen the 502 Bad Gateway in a few days either. The saving usually works after a while. Today I had to keep trying for about 2,5 hours before the design was saved.
As mentioned earlier it stops at random places each time.
I have tried saving while on WiFi, Cabled network as well as on cellular, but it happens on all of them so I don't think it's a connection issue on my side. I also set up my entire home network from scratch to eliminate potential sources for unstable network.

I am not saying that it is on your end but this is something which is out of my hands as well. Network and server is not something I have control over. It looks like the issues from last week are fading away.

@Scrubs Thanks for looking in to it. Its back again now, so I'll just try different approaches on my end.

EDIT:
Gave up on saving the build and accepted I will have to build parts of it again. Tried another browser (Microsoft Edge) and it works!
Note to myself: Frequent saving and switch between browsers saves the day 😃