I’ve done some research into this using Discourse 2.4.0.beta5 and there were no issues, I did find a bug that would cause the membership system to crash during the linking process which is now fixed and I will push that commit up, although not sure what the situation is with @systems these days if Jonathan wanted he could update to fix that.
I am going to move on to looking at the discourse service which basically is the code which syncronises groups of members, however I am suspecting there might not actually be an issue with the membership system but that Discourse has gone extremely wonky.
Would be nice to hear from the @directors about this as this has been an issue for some time and I am happy to help but I guess we need an answer.