I don’t have any certain info on the problem, but found this thread.
As for second issue, job switching should not be a problem, as far as your ARC is not canceled in between, and you keep the same ARC. This is I’m sure.
As for work based ARC to marriage based ARC and vice versa, I have heard mixed info. Many people say it is start over, but the OP in the thread says differently.
6 month extension, I’ve heard it can be a part of 5 years, but it is not a confirmed info,