At this time, when navigating to Plan settings -> Work in your plan, we can see the number of Work items, Boards, Spaces, and Filters.

However, when Spaces are not directly added to the plan but rather through a filter (or filters) or boards, the number of Spaces returns 0. While this might not seem like an issue at first, given that the number of Spaces is going to exceed the current hard limit of 100 (ref. limits), the plan will no longer load. Additionally, no warning message is displayed when the number of Spaces added indirectly is nearing the limit.

The plan can be accessed again after adjusting the filter, but only in a scenario where the plan's administrators know that the filter is the actual root cause.

Please consider adjusting the UI to reflect the number of Spaces added to the plan, even if those are added indirectly via boards/filters. This will help maintain a clear overview and also prevent the aforementioned scenario from happening in most use cases.