@aaribaud-fgs @dregad would be good if you could have a look at this.
I don't have time to have a deeper look, but I am asking myself if the new is_null checks are right. E. g. isn't !is_null( $p_show_disabled ) always true?

Bug confirmed. I'll have a look.

Proposed fix https://github.com/mantisbt/mantisbt/pull/2027

Testing and feedback welcome.

@atrol I noticed you targeted 2.26.4 for this fix. With 2.27 just around the corner, I was not actually planning on releasing another hotfix for 2.26 branch - IMO it's not worth the effort.. Would you agree to change target version to 2.27.0 ?

Would you agree to change target version to 2.27.0 ?

@dregad in my professional environment, the anser would be "no", as I don't like telling customers to upgrade to a fresh x.x.0 release to fix a major regression.
In your / our situation, the answer is "yes", due the little spare time we can invest.
If more users should ask (issue was triggered in forum), we could provide manual instructions how to fix it.

Good afternoon, everyone.

I reported the issue in the forum and, yesterday, applied the proposed fix from note 0069163 by changing the necessary lines in core/project_hierarchy_api.php. The previously disabled projects are now visible again. Although I couldn't test the performance under heavy loads since our projects don’t have any subprojects, it is working as expected. Thank you very much for taking the time to verify and fix the issue.

Thanks for the feedback @evanegas.solinfo