Certain tapes not written to after initial writing and before appendable date setting

In my organization, I have two HP MSL4048 tape libraries containing two Ultrium drives which uses LTO7 tapes with a capacity of 5.47 TB. The firmware for both libraries are the same. The Use Appendable media setting is 14 days.

For the two years, for one of the tape libraries, about once every two months one of the empty tapes gets written to but it doesn’t fill up to the capacity. And if in three days the tape is not written to, then it will not be written to at all and will choose a different tape, even though it’s before the appendable setting of 14 days, and its media info properties clearly states Yes of it’s appendable. The other tape library on the other hand will always fill tapes to its capacity.

Attached file no_writing_prematurely.jpg shows such an example. The last time it was written to was on 12/6/21, and the tape is not full and there’s 7 more days to be appendable. But it will not be written to at all. As mentioned, this occurs about once a month with a random tape. I wonder if there’s additional settings that I should be aware about.