I don't think I've seen this mentioned before.
I was trying to set up a schedule of six events on the first Tuesday of the month, starting 3rd September 2024.
To do this click in the "Repeat" field, choose "Custom" from the drop-down list and click the various boxes/fields then click the "Save" button.
The schedule was set up for 6 events on the 3rd of the month, not the first Tuesday.
Mods, please add this to the fault list.
I'm using a laptop, Windows 10, Chrome latest-ish build and BT Webmail 3.6.0