TL;DR: If you are having problems with a complex SVG crashing Inkscape, try cleaning up document before your next attempt at whatever you’re doing.
So I was trying to ungroup items in my svg, which contained a lot of groups (like 90+).
I selected all and ht ungroup. Instant internal error crash.
OK, I restarted. Opened the file, tried again. Crash.
OK restart, select one group. Ungroup. Crash.
OK I was about tired of this. I went in and selected one path, and tried to select same fill, then cut/paste to put it outside of the group. CRASH.
So, then I decided to try “clean up document”. Once I did that, i resaved (didnt seem to be necessary but you never know), and then selected everything and ungrouped. Success.
My svg had been edited and abused a number of times, lots of things cloned, uncloned, grouped, subgrouped, deleted, cut and pasted. There was probably some major junk in the svg, clean up seemed to solve my issues.