When I set up Fulcrum, I had a similar experience. I tried using the experimental fast mode, and it would crash after days of indexing.
Finally got it to work by NOT enabling fast mode in the config.
Discussion
That makes sense. My understanding is that fast-sync holds more in memory. So if there's a sudden crash, the current progress has nothing on disk to recover from. I think I only saw about a 20-30% difference with it enabled. Not worth losing more days over.
Yeah, give it a shot without the boost. I think that’s what causes the crashing. At least it was in my case over a year ago.
ElectrumX continues to treat me well, except for the undocumented biannual database compaction issue.