One of the causes may be that the appliance cannot get rid of its heat. It is possible that there is a blockage in the hose due to, for example, too many bends and/or sharp bends. A hose that is too long (by extending the original hose) can also be the cause.
Another cause is that the warm air cannot escape because the hose does not hang out or is constricted.

Attention: Always use only the original, supplied hose and make sure that it is placed directly outside. Using another hose or extending the original hose may cause a malfunction and will invalidate the warranty.