FMLA, short-term disability, maternity leave, and COBRA

I want some info before talking to the benefit team at work. I had a baby August 9th and have been on STD since then (it’s just over six weeks now). With my company I also get another four weeks of maternity leave after that. I’m returning to work remotely on October 17th. I did all the necessary paperwork for all the leave and FMLA stuff. It was a nightmare because I honestly do not understand a lot of the jargon. But everything went through good and I did everything I needed to and it seemed all squared away. I get paid 100% throughout my STD and maternity leave I should mention.

I got a letter in the mail today from COBRA/my company saying I was lost my group coverage on August 28th and I need to enroll in COBRA because I’d reduced work hours. I’m honestly so confused and can’t find an answer online. Im not getting terminated, I called my boss today and he was confused as I was and in fact told me I was getting a raise this month (so some good news). I have a difficult time talking to the benefit team at my company because I feel they’re not thorough. Is this normal? Did they fuck up somewhere and press the wrong button? Thanks for any info.