I’ve run into the same issue I suspect. The size of our model is about 1800 unknowns in its initial form and about 260 after structural simplification.
Today I tried updating our packages and suddenly the construction of the ODEProblem takes a very long time (structural_simplify doesn’t seem to have big changes). In the end I just killed my terminal because I did not get any results.
Here you can find the manifests from before and after the update:
Manifest before update.toml (123.2 KB)
Manifest after update.toml (122.0 KB)
Regarding the comment of @ufechner7, SymbolicUtils was 3.7 before the update and after the update it’s 3.27 so that might have something to do with it.
Our repo is currently still private, but I could try to create a flamegraph, or give you access to the repo to check out the issue?