There is a bug on ES 3.1.9. This is present on stock installation so kindly test on your end.
In Settings > Users > Profile Type > "PROIFLE_TYPE" > Groups
I see you can set groups to which members of this profile type will be assigned. However, if you also have this profile type require admin activation, then the user will not get added to the group. I have tested this and the only way the user is added is if admin activation is removed. This seems to be a bug.
Any chance this can be patched?