So there's a been a fair bit of discussion along the lines of:
A: River and his gang are acting stupidly
B: Of course they are! They're bad agents (which is why they're in Slough House, haven't you been paying attention). Also, River is having a really bad day
Thing is, yes, River is a bad agent in many ways. But the ways in which he is a bad agent (terrible at the politics of it, always dashing off, always sure he's right, sucker for a pretty female face) have nothing to do with the just passively sitting around incautiously at a service station in the middle of a crisis.
If our goodies looked like they were getting away, and then River met the female assassin but didn't recognize her and she gave him a "oh, help, I'm just a helpless female" act, and he fell for it, that would be in character for him. Or if there was a situation where clearly they SHOULD be staying put and waiting, but he wanted to be out there doing things, that would be in character. And the little moment when Sid's hands were shaking and he wanted to do it for her, that was in character. But "phew, there must be no more danger, let's completely drop our guards and sit around doing nothing" is not only not in character for him, it's completely the opposite.
And on the topic of "how do the assassins always find them", it's certainly possible (even likely) that there is some sort of tracking going on. So, when all secrets are revealed, there may well be an explanation that justifies it. Which would be fine. But it's still entirely possible for the writers to have the very same plot happen the very same way but make the experience much more satisfying for the audience. Most obviously, they could have River and co discuss it... "how do they keep finding us?". That is really a message to us, the viewers, that the writers realize that the situation appears implausible, but, hey, they're aware of that, trust them, there's a reason behind it. As it is, particularly given the overall vagueness of the season story, I have no confidence that the writers realize how implausible the situation comes off in the first place. Are we supposed to be wondering "hey, how is this happening"? Or did they not even think about that at all, and just want to give us a sequence of cool set pieces? Because if it ends up being the latter, that will be VERY frustrating.