This allocation error comes up from time to time. Is it possible you’re loading rds files with old saved fits in it?
That’s will cause problems. See here. Edit: I think if it’s old rds files that are failing to load you’ll need to rerun these fits with your new rstan install for it to work.
If you just copy-paste the code and data for eight schools from here does it run: stat_comp_benchmarks/benchmarks/eight_schools at 64b6597cd17de77e91dcfb1a9977758407017d20 · stan-dev/stat_comp_benchmarks · GitHub ?