When I was discussing this with him on Discord, it appeared it hit a hardcoded ‘give up’ time duration. His machine has a slow connection and its a slower device, but even if it takes hours for the fast catchup that’s nothing compared to the time it would likely take his device to catch up from scratch (and pruning the whole way).
Assuming there is still ‘activity’ it should never reach a stop-dead total elapsed time wall, throw away all of its work and start over not using fast catchup.