Thanks
I'm on Amsterdam now so I'll try Germany and see what it does. It behaves much the same directly connected to Nicehash and MiningPoolHub though so I don't think its an MRR thing. It seems, from much searching, that the specific error is unique to XMR mining, although that may just mean that Cast-XMR is a fork of XMR-Stak since they both have identical error message text.
I've switched to Stak again for a while as that has configurable error settings and better reporting than Cast, at a cost of 2-300H/s, so I'll hopefully get a bit more info about whats going on.
I had a really bad rental yesterday (only my 3rd too!). It was unable to connect most of the time so only got about 50% average hash rate. I asked MRR support about it and they terminated it exactly like you said. Having a backup card to boost the hash rate is a good idea. I could use my 960 for that since it can do about 8-10% of the Vegas.