Sadly this is the norm now with High Sierra.
You have a couple of choices.
1. If you really want to use Time Machine get a USB drive and plug it into the MBP and use it as the target. TM is much more reliable to local cf network targets.
2. Reset the Time Capsule. If you want to keep the old backup then I advise doing an archive to a USB drive (equal size to the TC disk).. then erase the TC disk.. reset it to factory.. and do a full reconfigure.. use all very short names.. not Apple recommended ones.. no spaces and pure alphanumerics.
Select this new target and start TM.. be warned it is very likely to happen again.. it might be a week or a month or even more but it will eventually wipe out its own backup or mess up its settings.
3. Use a different backup software.. I recommend Carbon Copy Cloner. There are other like superduper which is also popular but I found CCC best combo of price/performance/functionality. (no commercial connection).