I mean, it does not feel like it's broken, it's definitely syncync as the NAS is basically unusable now and working on the laptop is a pain. It's just slow. Extremely slow. Couldn't perhaps Windows Defender or firewall be interfering with the process?
I dont recall anyone complaining about that in recent memory. At this point you should ask Core directly.
Has to be a good reason why this can fall over in this way.
LevelDB is flaky on Windows. It has gotten a lot better with the years but a bad shutdown or basically anything else can completely destroy Core's DB.