Failsafe is overzealous

### Which version of floccus are you using?

5.7.0

### How many bookmarks do you have, roughly?

317

### Are you using other means to sync bookmarks in parallel to floccus?

No

### Sync method

Nextcloud Bookmarks

### Which browser are you using? In case you are using the phone App, specify the Android or iOS version and device please.

Firefox

### Which version of Nextcloud Bookmarks are you using? (if relevant)

n/a

### Which version of Nextcloud? (if relevant)

n/a

### What kind of WebDAV server are you using? (if relevant)

_No response_

### Describe the Bug

Even when just adding or deleting just a few bookmarks the failsafe kicks in.

### Expected Behavior

No failsafe.

### To Reproduce

?

(... waiting for a log file of the affected person)

### Debug log provided

- [ ] I have provided a debug log file

No files, tests, or entry points are named. Start by reproducing the issue in floccus 5.7.0 with Firefox and Nextcloud Bookmarks, and obtain the missing debug log; done means explaining why a small bookmark change triggers failsafe and correcting that behavior.

Written by the indexing model from the issue text.