I keep my core on an external hard disk and I feel sometimes the cable bends so the connection isn't 100%...
That's the reason mostly.
Core needs a continuous connection to the hard drive when syncing the chain.
Losing connection can lead to a corruption of your data, which does result in rebuilding your chainstate.
long story short it's now reindexing blocks on disk... which doesn't mean downloading the whole chain right?
Yes. The files are on your hard drive (except for maybe a few corrupted).
Those are being processed by core now, the missing/corrupted will be downloaded again.
I can see wallet balace to 0 but there's a list of recent transactions which are right, so it's just a matter of waiting, yeah?
Yes, simply not synced yet. Nothing to worry about.
always living on the edge with bitcoin! hehehehe
Not really, you just need a backup of your private keys. Then you are fine.
Your private keys are needed accessing your bitcoins, not any software or file.
