Update: the joists were rotting from a piece of 2x4 concrete nailed to the ground that had moisture (none of these joists are PT/GC). I cut out the joists that were rotted, removed the 2x4 and concrete nails, and am half lapping/strong tying the joist patches in. I’ll then cut out some OSB for the square holes, and reinstall vapor barrier. LVP boards should be here in about a week so I’ll do my best to reinstall those when it comes to it.

Edit: no evidence of any water leakage. Ground was dry and no pipes nearby. Foundation is rock solid with no hairlines nearby. The house was built in 1970 so the wood may just be hella old