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. :)
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.
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.
Retention decreases exponentially with temperature, but the flip side is that it also increases exponentially when refrigeration is added. A conservative estimate is 30 years at -20 Celsius. Another added benefit of flash is that it's now much denser than tape (~10x) and doesn't need to be moved - it can be powered down on the storage rack (and powered up for refresh every 6 months or so). Unfortunately, it's still ludicrously expensive (and even more at the higher densities).
—which happened often enough. Tape stuck in a drive, operator has to go into the tape library to fish it out. You have to turn the robots off first. Individual tape errors were invisible because we used erasure codes. We would have to see, like, four correlated failures in order to lose data.
I did the math and we were comfortable with that level of redundancy, based on our data for how often tapes fail. When I say I did the math, I mean I personally did the math, but I don’t have the figures handy.