CPU spike when saving project

Our project has been suffering from frequent CPU spikes when saving assets. It seems to happen most reliably when the project is saved the first time after exiting playmode. Subsequent saves are faster, but going into play mode and exiting causes the next save to take up to 10-15 seconds.

I've profiled the editor during a spike:


It appears the major offenders are internal Unity processes. I should note that there are no user created AssetPostprocessors in the project, and the Editor folder is empty except for Unity's own ImageEffects. I'm mentioning this because there seems to be a lot of time spent within the foreach loop of GetMeshProcessorVersions(), which I suspect means there is something in EditorAssemblies that it's cycling on.

Any idea what the issue is? Any help would be much appreciated as this is slowing down our workflow.

TIA