I see calc fields get hung up occasionally this happens at times when the system has a spike on the "Background tasks: data export, import and calculations" chart on the status.podio.com page.
Obviously, the more complex the calculations the more likely they will fail or I suspect more specifically timeout waiting to run.
In these case, you either are left with an old result or in cases where there was no data there before a blank field. There also is no way to know this has happened other than the wrong result.
Since calculation fields only trigger or are updated with something changes related to them past a timeout nothing will recover the problem except making a change that would update the Calculation and or making a tiny meaningless modification to the calculation formula.
I have actually thought about suggesting a way to trigger a re-calculation of all fields in a single record (which would be lower impact than editing the formula and causing all the items in an app to attempt to update).
Not sure this helps you other than to acknowledge it is not just you.