Recently my charger hasn't been fast charging so when I charge my phone the battery would still be draining even when it's charging without me on the phone. Or it would stay on the same charge overnight. I actually factory reset my phone and the fast charging started working again, but once all my back up data upload back on my phone it stopped fast charging.
Strange, I would think it might be a cable issue (which was what happened with an old LG I had) though if restoring your settings is causing it, I would check to see if fast charging is enabled in your settings. The symptoms you described sound a lot like what I was dealing with my LG, which would burn through cables and eventually burned out its USB port. It might also be the charging adapter going bad.
My S8+ has had the same issue for 2 weeks now. did a reset and restore, and nothing changed. The place I got the phone from is convinced it's the charger, or my outlet I'm plugged into. My outlets are fine, and tried another wall charger for this phone and got the same message of slow charging. funny but my after market car charger works just fine. looks like this is an ongoing problem if you Google the issue, and nobody wants to fix it.
Sounds like something in your data may be corrupted. Try a reset but instead of reloading your back up trying doing new downloads of your apps. If everything works then add your backed up files slowly to see if they cause the problem. Almost forgot...after fresh install download antivirus and security software.