What do you guys think about a "middle" developer from one project taking a "junior" position in the other project?

Do projects have static roles or something that mean something?

I'm not a job title kinda guy. I don't worry about that do much, but I figure job titles would mean something...not the job.

@N00bPancakes afaik, titles do not mean much, but I'm not sure.

Junior in the sense of title / pay, or junior in the tech being used for that particular role?

@C0D4 probably the latter, because there's a substantial shift in technology between those projects

Title as well, though no info about payment

@iiii then no, if the dev has limited experience in that stack so be it, a lot of the devs knowledge should be transferable though and will probably pick things up quickly.

There's nothing wrong change stacks, I've done it a few times.

I wouldn't.

One of the qualities of a junior is being slow in adoption o new/different technologies. If you're a mid, I'd expect you to be quite fluent in this sense.

Unless there is a possibility to agree that I'm a junior for like 3 months and then I'm treated as a mid again.

Also, I'm one of those people who believe a job title matters. It's a lot easier to get recruiters'/HR attention for more serious/interesting roles when you're not a junior.
"this guy has been a junior for 4 years. Clearly there must be smth wrong with him... NEXT!"

Care less about titles. Care more about whether you find the work challenging and enjoyable. I’ve had a director title at an ad agency and all we made were marketing and product websites. Had a “regular” dev title and worked on integrations. Decide what is important to you- your skills or your title.