Looking at reports from across the web, looks like soulbound and the inventory chest on death possibly have a conflict. It looks like a bug in the modpack itself. As this is a packaged modpack, I can only make changes to the config and not fix the issue itself.
I’m doing a server migration at the moment, but yes I can reset to an earlier save. Backups are every 3 hours, 12am, 3am, 6am etc…
Although I may change it in the future as that world is getting quite big.