there is a weird bevavior in EOS beta 3.1.5b4. When there are submasters 11 to 18 and one deletes 14 thru 17 and then accidently again deletes 14 thru 17, submaster 18 vanishes.
(Seems like the video does not play always or is not shown at all, maybe there: https://my.hidrive.com/lnk/qOSzGWIW)
If wanted, I could share my showfile via private message.
Thank you for bringing this to our attention. We have reproduced this and are tracking it as [EOS-53883] [Subs] Repeated delete of range of subs deletes the next sub outside the range