Is there any heating issue with OnePlus 5 ?

Well, there have been a few initial reports - or complaints rather - that the phone gets heated up while using apps like SnapChat or YouTube. Please note that the apps mentioned are quite heavy on resources . If one or two such apps are open and working in the background, it is quite natural for the phone to get heated up.
There have also been few reports that indicate that the phone gets heated up near the camera module. If the temperature goes up by a few degrees, it may not be a concern. If it, however, becomes a regular phenomenon, you may need to consult service or get your device replaced.

Yeah, Some users had experienced the heating problem of OnePlus 5 while using heavy apps. The area around the camera region can be felt warmer than normal during using those apps. It's no such a big issue you can cool down the phone by keeping it away for a while or can contact the customer care to get the phone replaced if the phone has started heating up from the day you purchased. You can switch off your phone to avoid further heating up.

For moderate usage the phone One Plus 5 is reported as a normally working. It is only when it is heavily used that there are some mentions regarding overheating and fast battery depletion.

These are stray cases as reported in One Plus or other forums.