Hostile work environment when returning from a medical leave of absence

Approximately 3 months ago I went on a doctor & company approved medical leave of absence. Prior to leaving I was working anywhere from 60 to 90 hour work weeks. Not uncommon for our global company. I often mentioned to management that the pace was completely unsustainable, and that I was fast approaching burnout. My manager agreed the pace was unsustainable, that we were all working more hours than was acceptable.

The leave of absence was a combination of working insane hours, depression, (due in large part because of work), personal life, etc, and just exhaustion. Prior to leaving, I was considered the senior person on the team, reporting directly to my manager. Meetings, projects, reports to my manager were part of my daily duties.

I was concerned about leaving for the FMLA, I verified with my HR department that this would be confidential, and that my team would be told that this was just a leave of absence and nothing else. They verified that this was the case. Then on a public call spanning various departments the Director announced I would be going on a medical leave of absence on Dr’s orders, and that I would be letting them know if I can come back early, blah blah blah.

Utterly mortified, I went to my HR department and was told if I had an issue with it, I should talk to a different HR person. My leave was starting, so I decided not to make a huge issue of it, even though, I probably should have.

My manager went on to say to me privately, that he’s required to let me return, but not necessarily in the same position. The general implication was if I left, who knows what I would come back to.

This is my 2nd week back. Upon returning the environment is definitely much colder than when I left. My emails weren’t answered upon return, my accounts were left locked, I was unable to do any work until the 2nd week of my return. At which point I was told that I would now be reporting to someone clearly my junior on the team.

I know this is a lot of random information, and it's hard for me to articulate if there's even an issue, other than it being an unpleasant working environment. I have no idea if this is perfectly legal, and that there are no issues with it, and that I just need to deal with it, given that I understood the risks going in, and the probability of returning.

Thank you in advance for any information and advice.