I have been repeatedly getting this error while uploading larger fseq files from FPP Connect. It happens almost everytime I render and upload a sequence. To get around this, I have to keep re-uploading from FPP Connect until it works. It is not crashing xlights, just an annoyance. My controllers and network configuration are the same as last year and I didn't have this issue last year. The one difference is I am running Windows 11 on my Xlights machine.
So I know you are going to need some diagnostic information, My ask is what specifically do you need. I added the log files and I am using xLights 2021.34 on Windows 11