I investigated, and it's a recent bug introduced in LR 7.3, 7.4, or 7.5: Address lookup overwrites an existing altitude recorded in the imported photo. If you turn off address lookup in Catalog Settings > Metadata > Look Up City, State and Country..., then LR will import the existing altitude and display it in the Metadata panel.
Please add details of your issue and your constructive opinion to this bug report: Lightroom: Address lookup overwrites existing altitude | Photoshop Family Customer Community . Be sure to click Me Too and Follow in the upper-right corner. This will make it a little more likely Adobe will prioritize a fix, and you'll be notified when the bug's status changes.
I see. Well, if it is a bug, let's hope they fix it. Thanks a lot for your answer!
I have the same problem. I use drones and when I import the photo, the altitude is changed. Lightroom show the same altitude for all files. Even if I import from a disk or SD card.
I did another test. I imported a file with Lightroom, then I copied the file manually, afterwards I read the metadata again, and the altitude was good.