Just to be sure you've got the idea: it is not too big problem not to get response or get buggy version (read as 'not tested well') if we talk about cheap home routers. I also understand MT is a small company where too few people can pay their attention to improve anything, while they keep adding new features that's demanded on market.
So to say, as you add new code you can't lower bug level in whole ROS image at once.
But as I try to treat MT as SOHO devices we can trust then I start to treat MT support as weak and often silent. It is a bit dangerous to use MT devices in serious networks due to MT "policy" (habit?) of their communication with their loyal community.
It is good to know they managed to sell their devices in Africa, but I'm not from Africa and still I'd like to get support, am I wrong?
https://en.wikipedia.org/wiki/MikroTik# ... IT_markets
But you said you resolved the problem for yourself when you upgraded to RC version??
Also I'd recommend you stick to Bugfix release as I would like to help you but I do not have the faintest idea of how to replicate the issue that you had with pptp. I am running a variety of pptp, l2tp etc and on version 6.34.2 with no issues.
So my guess is this could be an isolated issue on your setup perhaps, or maybe a genuine bug but there is no way of knowing and the best thing to do is to follow Chaos's advice with supouts and detailed description with perhaps log errors to show how this issue happened or at least help MT or us on the forums to reproduce this issue so that a solution can be made. Be it temp then permanent.
Thanks