Just a thought, I don't know if it matters or is relevant, but are you using new SD cards, or ones that have been used before?
I seem to recall there may have been an issue with some cards not being fully re-formatted with some systems and the usable size went down gradually. This may result in things being put in the wrong place on the card. Not normally important, but may be in this case. Maybe someone with more knowledge can help on this.
There is an application on RacyPi Distro for PCs that I have used to look at partitions and move or delete them.
I used a Live CD version I downloaded from somewhere a while ago, so normal PC not affected afterwards.
since all work gets lost
If you don't have a spare USB slot, you may be able to remove the keyboard, or mouse as necessary at the time, insert a memory stick and use the mouse to save anything and restore it later. Not ideal, but should work. You can find a formatting tool under Utilities.Caution.!HForm.
As I'm swapping different SD cards and reflashing occasionally, I have a USB stick always plugged in and save anything I want to come back to, there.