I do run into this - and when i do, I try to ask myself: *why exactly* are those particular bars a problem? Sometimes a bit of musical analysis helps me.
I've just had to learn the Arrival of the Queen of Sheba in a hurry - in two weeks, for a friend's wedding. There was one passage of four bars that I could get up to a certain speed (so I realise - not exactly the same as your problem - but I think the example still may be useful), and no further. It was as though the signals from brain to fingers just totally became rubbish. I wasn't even playing wrong notes that were wrong because my finger slipped one sideways - it completely disintegrated.
I got a bit fedup with this so I tried to see if I could work out what the problem was. In this case, it was because it was an orchestral reduction so the melody was going between the hands. I had not twigged that this was happening, and once I got that, I was able to "predict" what notes came next and it came together pretty quickly. It didn't mean that I didn't then have to practise it a lot some more, but that was what got me over that speed barrier.
I guess this shows me that for me anyway, there are two barriers I have to get over: One is "do I know what is happening musically", and the next is "can I make my fingers move in the right way to make it happen". Sometimes, I can skip the first to get to the second. I couldn't in this case.
I don't know if the same will hold for you, or if it does, which stage you're at, but perhaps it will be a useful different point of view