Is there a device number limit on a mobile subscription?

The last I heard there was no limit to how many mobile devices can use the same account. It's different for computers. Those are limited to 2 active at a time.

I use my account to download pics from my family members' phones. Never had a problem, but I only do it once in a while and they aren't actually LR on their phones. I just log in on their phone, choose the pics to sync and it works. I've unfortunately synced a bunch of pics more than once but that's on me - user error.

In my case, I use my user on my iPhone at the same time as on the Web and and iPad (the latter with a different iCloud user) but with the same Lightroom Mobile user. Once you identify a Lightroom Mobile user, the app syncs that user's data/images and, I assume, will delete what doesn't apply to that user. This means several GBs of data.

When you use different devices for editing, when moving from one device to another quickly, it warns you of the existence of unsynchronized changes and does not allow you to continue with the image until it is completed (it also happens with the use by the web), therefore, I understand that it is possible to use several devices at the same time but only one user (with the consequent synchronization of data / images of the user that I mentioned above)

As far as I know, a single user.
Maybe multiple devices.
The FAMILY option does not work.

As far as I know, there isn't a limit.