I forgot to edit my last post. Case's closed, everything works properly! Thank you vv181!
That's good to hear, but before you lock the door on this thread, I'd like to mention that I see way more HDD failures / corruptions / issues with Raspberry Pis than with normal PCs or laptops, where this type of stuff rarely happens. I'm not sure if it's because small corruptions just aren't normally noticed (because files still open fine, ...) or because the Raspberry Pi node operators are not supplying external power.
My personal gut feeling says it's the latter; in fact, I've had this issue myself in the past. I had a SATA-USB adaptor with barrel jack for external power, as well as a powered USB hub that I tried to use with a USB HDD and both failed sooner or later. Back then I had no USB-ammeters on hand, but I believe if you have such issues, it is worth measuring if your specific HDD / hub / adaptor is pulling most of its current from the Pi's USB socket or from the wall.
The reason I suspect this to be the common issue is that the Raspberry Pis provide extraordinarily low output on their ports; for a long time it was just a few hundred mA. It might have changed with the model 4, though. On the other hand, a laptop or PC tower is specced to easily power the SATA ports that it has.