This was caused by 91de4a50ab refactor which replaced
the evaluator cache singleton by local variable.
It was unknown that the evaluators in the cache
are actually referenced by the modifier data.
To fix this and fix the thread-unsafety of the global
variable, a mutex is introced around a reduced critical
section inside `draw_subdiv_create_requested_buffers`.
The global evaluator cache is now also refcounted to allow
freeing of the cache when no evaluator is referenced
anymore.
Pull Request: https://projects.blender.org/blender/blender/pulls/134926
a79bc953d3