Remember the audience here is users, not developers.  I'd suggest wording such as:
```
- Fix a problem when converting to a `TimeFromEpoch` format (`unix`, `cxcsec`, `gps` or `plot_date`)
  when the time scale is `UT1`, `TDB` or `TCB`. [#1732]
```
I also think you don't need reference the original issue but just the PR that has the code.  Any interested user will find all the github cross-references without trouble.