Slitherine

It is not possible to upgrade Sturmpanzer I in the deployment phase.
In fact, trying this will block upgrades of any other unit as well.
Save game attached.

The scenario is part of a custom campaign.
If you need the whole campaign, there's a download link in the first post in this thread:
https://www.slitherine.com/forum/viewto ... 64&t=98862

Haven't checked the save yet in detail, but had a quicktest from editor with newly purchased StuPzI. That was able to upgrade, in deployment and on-map. So there's no basic prob. Will check the save throughout the week.

This unit got a data change recently (intro date), but normally this should not affect upgrading.

May be correlated to this:

(Unit Bug) (Purchase menu wont open) (8.4.1)