TimeMachine backup problem

Hello,

I have got the following issue with my TimeMachine backups. I am using an external 2TB HDD, which is connected to a USB switch and used on 2 different machines (my primary MacBook Pro and my secondary PC). It's formatted encrypted APFS volume and used mostly for TM backups (with some of my manual backups too). Now the problem - I used it many months without any issues, but now I see that TM shows me "Last backups: no, Oldest backups: no" and it can't create any new backups because there is not enough space on the HDD. Obviously it can't access the older backups at all, even though I can clearly see all the directories, browse them etc., and even open the sparsebundle files in the recovery mode (Cmd+R). I tried to use "First aid" in DiskUtil, it ends with "failure", then I used the DiskWarrior 5.2 to fix the issue as well - it also ends with an error during Step 5 (locating directories) during the rebuilding. Probably I switched the drive to my other PC during the last backup and something got totally wrong since then.

My question now is - what kind of solutions are there to rebuild the TM backups? Can I somehow "re-initialize" them? Or the only thing that remains is to remove everything from the drive and reformat it? This would be bad as I don't have any other 2 TB drives left where I could copy/move all data to... Besides of it as I understand MacOS blocks all TM related files, so they can't be read properly. Sparsebundles are shown as "0 bytes" files with Finder, even though I can definitely go into them and see some content from Terminal in Recovery mode.

Thank you, any help is HUGELY appreciated!!

P.S. I am using MacOS Mojave, not High Sierra, sorry about choosing the wrong topic.