I have had similar experience building microservices that used shared repositories. The PR paperwork was so bad that at one point I've made all my services self-contained, just to avoid having to modify my own code in two different places and synchronize the changes.

The whole problem, I think, comes from the "split the code" cargo-cult. We need to think about why we're splitting the code, and use that why to figure out when to split code.

IMHO, code separation arises naturally from modular programming - once your code is mature enough, it becomes just a piece of glue around a set of libraries that you can just rip out and put in their own repos, provided that they're useful enough.