When you resync on death, your player data rollback to what it was before you first synced (or at least before you installed the mod). Which means that your thaumcraft researchs and your enderchest content (among others) get lost.

This also breaks Ars Magica 2 progress.

Should be fixed in Version 2.1.0. Please let me know if it still isn't.

still seeing a thaumcraft rollback on death with 2.1.0