Thanks for your reply, and sorry for the delay.
We established that the reason why we were seeing the above message in the cta-taped logs is because the retrieve space was full - cta-fst-gcd was not working because the EOS FS scan kept updating the files’ ctime (see our other post here, Tape aware GC on FST stopped working - #6 by george_patargias) - and also because of the fact that we had created a single back-pressure rule that affected both of our EOS instance.
We have created an additional back-pressure rule, modified the existing one and we got GC working again and the “Empty recall mount” message did not appear again.
George