Since the update in Battery Protection where there are now 3 options, I always choose Maximum. This is because the 85% before the update worked really well for me.
However, I noticed that using Maximum only charges my battery until 79% and drains fast to 75% after unplugging. I thought leaving my phone charging for a few more minutes would help it reach 80% (target level), but it mostly just stays at 79%. If at times it reaches 80%, it will easily drain to 77% after just 3-5 min of turning my phone on. I never had this problem when Battery Protection only had one mode, which charges up to 85%. Back then, I feel I can really maximize my phone usage even though it's just 85%.
Have you tried a factory data reset? Backup your data using either a usb-c flash drive with Smart Switch or another phone or computer, also using smart switch. Then try to factory data reset. After that obviously put your data back on your phone, and wait for about 2 weeks if you are still seeing that at that point, I would say contact Samsung customer service.
