I am seeing not only large index directories, but also an enormous number of files in my index. Here is a raspberry pi running (only) syncthing, with over 2.4 million files in the index folder. I had another pi with over 3 million:
pi@pijeffoffice:~/.config/syncthing $ du -h index-v0.14.0.db
12G index-v0.14.0.db
pi@pijeffoffice:~/.config/syncthing $ ls -fl index-v0.14.0.db | wc -l
2457856
pi@pijeffoffice:~/.config/syncthing $ syncthing --version
syncthing v1.3.1 “Fermium Flea” (go1.13.3 linux-arm) deb@build.syncthing.net 2019-10-07 11:30:25 UTC
Before I do a -reset-database, is there anything you would find useful?