Can't change the Activity type in first leg of converted multisport activity

Did a multisport event : kayaking / running / mountain bike.

Had no idea how to record it in Garmin (Venu 3S) so just set it on Walking and off I went.

Later when looking at it, I realised I can convert it to a multisport event. Great!

So I can divide it up and create the three separate legs just fine, but the first leg stays at the originally set "Walking". Whenever I try to convert it to kayaking I get an error basically saying cannot save it, try again. But try and try I do and it does not save.

So I thought ok, let me change the whole things to kayaking first and then convert to multisport. Nope, cannot create any legs at all if I do that - get the same cannot save error, this time not letting me create any legs.

Any suggestions, ideas, bribes to developers are welcome!