Disclamer: I used Defold Engine 1.2.119 (2406775) so it could be fixed now.
I think that it is some sort of memory leak when having unsynchronized things for a long time, or the editor opend a long time. Yesterday I opend 2 prodjects and had no problem runnig them, but when I came back 10h later I had to close one and synchronize the other to not drop below 10 FPS (I wasn’t able to take a screenshot of the task manager because I diden’t have a hotkey for it and the FPS was so bad that I could not quick search and run the snipping tool)
Before synchronize after ~10h (One prodject) (0 - 10 fps)
CPU, Memory, Disk, Network, GPU
After synchronize: (less lag, but still around 20fps)
(The disk usage peeked at 12MB/s and the memory peeked at 1000MB)
After opening the same prodject with the same changes as before (Before synchronize, no lag)
After: (around the same stats as before, no lag)
I only chaged the posision of an gui node and version number (only had the gui and game.object up, closing them did nothing). When restarting everything ran smoothly. I think that the amount of time spend in the editor has to with this because I only got the problems a few hours in, and can’t replicate it with a editor that has only been running 10min.
I don’t know if this has been fixed and the numbers I have given are just one screenshot. I have to do more testing for more reliable results.