I had this problem at a live stream. I noticed the cache was filling up quite fast during testing and tried different 4G hotspots but it didn’t seem to fix the problem. A speed test showed there was ample upload speed available (20Mb/s). I reduced the quality to Streaming Low and still no help. I wish I had tried reducing the frame rate from 50fps to 25fps but didn’t. It ended up with the stream stuttering for a lot of the time.
At the end of the stream I tried to stop the stream by pressing off on the panel and in the software but it seemed frozen. I suspect it wasn’t going to respond until it had cleared the cache, but couldn’t because it of the upload problem. I ended the stream manually on FB and after waiting some more, eventually had to cut the power.
Unfortunately this corrupted the USB recording so I lost that too. I haven’t been able to find any info on the problem which is a shame - hopefully someone smarter than me comes across this post!