Catch-up occasionally ignores start date

### Site

phanpy.social

### Version

2025.11.26.ac85274

### Instance

social.seabass.systems

### Browser

140.0 (64-bit) on Fedora

### Bug description

I frequently use the catch-up feature with "Until the last catch-up" selected. Occasionally, it ignores the date/time of the last catch up, and instead fetches thousands of posts dating back months.

### To reproduce

Can't deliberately reproduce, but happens frequently.

### Expected behavior

The date/time of the last catch-up should be respected when "Until the last catch-up" is selected.

### Other

`social.seabass.systems` is a self-hosted GoToSocial instance with one user (myself). I have access to the logs.