Strange behavior of the laser beam (80W Red chinese)

I have a small problem with the chinese 80W laser, 700x500mm.
I have noticed a drop in power, little bit. The laser beam at the end of the tube escapes to the sides.
I posted a video on youtube. link below. Tuba has a maximum work time of 20 hours. I am a hobbyist and I cut a dozen or so elements a month. Does this mean tube wear? Or sometning else…
date of manufacture of the tube 09.2019
I use a chiller 3000 for cooling, the working temperature is in the range of 18-22 degrees Celsius, max current 23 maybe 24mA.
Anyone had a similar problem? Any ideas?
I will be grateful for the hint :wink: