Perhaps one of you is living in a much more humid and/or hot environment that causes issues with the writing process.
Debugging this was really fun, especially due to the randomness factor. :)
Understanding why this is as important as it is requires some visualization of the bit densities of modern tape drives, the capacity is enormous, the tape is ridiculously thin and the bits are small enough that it doesn't take much to make a part of a tape unreadable beyond what the error recovery logic can deal with. And that's before we get into longer term effects such as layer-to-layer copy and demagnetization.
I suspect that the number of problems you encounter from tapes scales superlinearly because they physically move. This leads to a lot of unpredictable failure modes. HDD racks also fail a lot, but in more predictable ways because all the data is managed in software.