Reproduced in SRP master of 7/29/19 (afc7c3f3a9), Version 2019.3.0a12 (7584d9f005ad) Sat, 27 Jul 2019 04:29:58 GMT Branch: trunk

Repro:
1) Select a group on nodes
2) Press control+g / right click > "Group Selection".
> Only one Node will be grouped.

Note:
If you then click "Delete Group and Contents" after step 2, it will delete all the nodes instead of the only that's visually in it.

Bonus:
Maybe take care of this https://favro.com/organization/c564ede4ed3337f7b17986b6/d06b8de3e40da6d340b5b063?card=Uni-96948 while resolving this? :P