I can't seem to find any other reports of this odd behaviour, but on my S5 when I want to change filaments, hitting unload doesn't cause the hot end to heat up, it just goes straight to yanking the filament out of the print core, cold. This often causes a necking and snapping of the filament end, leaving a slug of old filament in the core, which then takes quite a while to flush through.
This can't be right, can it?
I also find that now and then the UI can get stuck waiting to detect something, like a new print core installation, which doesn't trigger. I've ended up having to power cycle the machine and try again to get it to spot the new core. Firmware is 5.1.8.20181207