@ydd:
Thank you for reporting back.
I was able to solve problem - removed all search paths from project. Strange that other installations did not have such problem on same project.
That is indeed a situation I can't remember having seen before, at least not with FPCUpDeluxe. I'll keep it in mind so thank you for reporting on that.
I do not see such option to select - I added screenshot with possible options.
The RC versions of Lazarus can be added manually to the basic lazarus installation tab from the tags tab. From that tab it is possible to manually select "tags" to be added to the installation list.
You are correct on the 3.8 version, as it is not specifically listed. That requires either a manual edit of one of the FPCUpDeluxe ini files or by setting the tag manually in the setup+ dialog.
Instead the 3.0 fixes should correspond to the latest Lazarus release (3.

but with fixes on top.
I tried this - did not help
Ok, thank you for trying and reporting. The 'fix' you applied is reason this does not work as the used path would still be wrong, even for/on a rebuild so in hindsight expected behaviour.
I'm doing so
Unable to tell but have no reason to doubt that. I mention it to just make sure the install path is properly set (and not install into a previously used install path). I personally forget to do that when using FPCUpDeluxe simply because I overlook it 9 out of 10 times (and I am therefor assuming others might (sometimes) forget to do so as well).