If you are trying to create a search of the Location post type which includes a filter for capacity (a field that is part of a repeatable field group) then it is not possible because it is not supported. Repeatable Field Groups are implemented as child posts and this effectively involves filtering by fields of related posts, which has not yet been implemented.
If it is the second case, I can escalate this thread so that it is attached to the internal ticket for the bug and I can update you when it is resolved.
I would search for Room(s) filtering it by its custom fields. And one of your colleague of the support wrote me that this feature where integrated in the 2.9 version of views
Unfortunately, as you will see in the erratum I linked to, it doesn't work. (I don't think it was implemented.)
The erratum is new. For some reason we haven't had people asking about this generally, but you are now the third person asking about it within a week. It has been raised with the Views developer, and I've seen progress in the internal tickets, but it isn't resolved yet.
Now that I know this is what you are referring to, I'll escalate this thread and attach it to those internal tickets, and I'll let you know when a solution is available, although I note the final comment of the developer is that it might take some time.
Just a quick update to let you know that this has been fixed by the developer and once it has completed testing it will be made available in the next Views update.
I don't have an ETA for that, but I'll post a reminder when it is released.
The update has now been released, so it should be possible to create searches of RFGs. Let me know if you still experience problems after updating, thanks.