Circular editing locks on all sequences

I have a team of four editors on a Team Project. We just finished a very similar Team Project without difficulty, but this new Team Project has run into immediate trouble. I would appreciate help from @Udo_Pawlik or anyone. Udo, I can invite you to the Team Project if you'll please tell me how.

The problems: 

• Premiere is showing editor 1 that editor 2 is editing every sequence in the project—but it's showing editor 2 that editor 3 is editing every sequence, a nonsensical circular ring of locks. No editor would be intentionally editing every sequence. Even if someone goofed with media mapping or relinking, as I've seen happen before, I don't think that every sequence would be affected.
• Last night Premiere showed me that one editor was editing everything, but now it shows me that a different editor is editing everything. 
• One editor reported that he had only just opened the Team Project for the first time when Premiere showed a "Save A Copy" dialog: "You have 1100 sequences with unpublished changes that were edited by your collaborators. Your unpublished changes will be saved as new sequences." He exited without publishing, tried again, and got the same warning. On the third try, there was no such warning, but (as in my first bullet) all sequences were being editing by another editor.

The project:

This project, like our last, has a large number of sequences (1100) but not a particularly large total length of video (600 minutes). Within the Team Project are essentially 100 little projects. Each has a main sequence with nine sub-sequences, one multi-cam sub-sequence, and two clips that are each three minutes long. The successful previous Team Project was organized identically and worked well. I created both from the same template by using the excellent Automation Blocks. When I click on Premiere's cloud sync icon in the middle of the title bar, it shows me a green check: "Project saved and synced. Last synced 4 days ago." 4 days ago is when I created the Team Project, but it's an oddly long time ago given that the four of us have all accessed the project in the last day and Premiere is showing locks. In Creative Cloud's notifications, I only see that each editor "has joined" the Team Project; it doesn't list that anyone has "shared changes" to it.

The environment:

All of us are using Premiere Pro 2024 v. 24.6.3 or higher but not 2025 (I've waiting for the other editors to confirm their specific versions) on a mix of Macs and Windows machines.

Thanks for any help,

Wallace