JulienM1 ... It happened to me and when I asked, I just got told everything was working fine. For me, it was happening intermittently.
My suggestion would be to keep track and then you have some examples, if you need to discuss with the techies.
What I did was keep a list of threads I was currently subscribed to and any new ones I added with the dates. Then for each, I'd note the date and post # 42 (for example). Then when I next checked I'd note the date and #43-#52 no auto-notice. Or if I received an auto-notice, I'd note the date and #43-#48 by auto-notice.
Life got too busy and I didn't keep it up. I "think" that I am getting the auto-notices, but not sure. Need to try to get myself into the regimen again and keep track!
Good Luck!
Keep that going for awhile and then you have some