Run core temp by the side of your browser or select 'always on top' under the options tab for now. You can then monitor your CPU. If it's getting hot, then you need to clean the innards of the PC. Straighforeward if a desktop. Common sense applies but if you need a bit of guidence we'll be happy to share how we do it as cheaply as possible. Usually free.
HTC U12 Plus review: Hands-on