This isn't actually a problem! We build gas pipelines all the time which suffer exactly the same problem. (and no, you don't want gas pipelines to leak!) You can use expansion joints, or grooved couplings that enable movement, and there are other solutions as well. I think the problem that people have is that they assume you need some really intense vacuum for hyperloop to work. .05 bar (the pressure at 60,000 ft) is fine, and so is some leakage into the pipeline, which you just have to pump out.

Normal pipelines handle large amounts of thermal expansion in a way fundamentally incompatible with hyperloops: https://www.quora.com/Why-do-oil-pipelines-have-so-many-seem...

https://duckduckgo.com/?q=expansion+loop&iax=images&ia=image...

Why would that be fundamentally incompatible?

There are no expansion joints on continuous welded rail either.

The track is instead clamped so strongly that it can maintain its alignment even under thermal stress.

https://en.m.wikipedia.org/wiki/Track_(rail_transport)#Conti...

The tube could sit on rollers and/or the expansion could go into pushing arcs out slightly more. There are probably a lot of solutions.

It doesn't necessarily need to be a perfect vacuum. The less air in the tube, the less resistance there will be. I would guess there would be vacuum pumps constantly taking air out of it.