This is the problem with GT pipes. Each section of GT fluid pipe acts as its own tank, basically. It fills and empties, fills and empties, fills and empties over and over. If we could view inside each section of GT pipe somehow, I think we'd see fluid levels being different in each section, and we'd see the levels going up and down independently, almost at random.
So basically, I think what happens is, just due to these random flucuations in each pipe segment, there will be a time when all the segments are "low fluid", just by random... and at this point, the machines at the end of the line, down at the far end of the fluid pipe supplying them, well they're gonna suffer, they will have insufficient steam. Perhaps the kinda random nature of the fluid flow in the pipes will refill those pipe sections quickly. If you're not using max steam flow, then it probably will refill and you won't even notice. But it's also entirely possible that those end machines are now stuck in a bad endless loop where they just can't get enough steam anymore, due to the nature of how GT fluid pipes work.
My solution was easy, get rid of using all the GT fluid pipes and swap them out with Ender IO fluid conduit. When I do that, my systems that weren't working very well suddenly perk right up and work perfectly. GT fluid pipes, sadly, are just not up to the task IMO. But others seem to get them to work somehow, so I'm not saying you should give up on them, but I am saying you probably need to understand how they work and why they cause players problems. Hope this helps, and if any of it is incorrect I hope someone will teach us more about this common problem in the modpack.