Chkdsk ended after about a minute saying:
Errors found. CHKDSK cannot continue in read-only mode
The full scan says:
Code:Stage 1: Examining basic file system structure... 446720 file records processed. File verification completed. 33405 large file records processed. 0 bad file records processed. Stage 2: Examining file name linkage... Errors detected in encrypted file record segment 265947. Errors detected in reparse point file record segment 265947. An invalid filename x86_microsoft-windows-i...ntrolpanel-option8l_3dbf3e56a1364.35_41.0 (269051) was found in directory 45336. Minor file name errors were detected in file 269051. Index entry x86_microsoft-windows-i...ntrolpanel-optional_31bf3856ad364e35_11.0.10240.16384_none_5d536d65249bd25d.manifest in index $I30 of file 45336 is incorrect. Progress: 471109 of 562458 done; Stage: 83%; Total: 77%; ETA: 0:00:19... 562458 index entries processed. Index verification complete. Errors found. CHKDSK cannot continue in read-only mode. Failed to transfer logged messages to the event log with status 50.
For reference, I ran CHKDSK before I tried to Reset my PC and it did the hour-long scan and everything came back fine. Clearly something has changed.
Hopefully you can make more sense of this than I can.