Purple/pink pixels appear in dark areas

[radR]

Philips 50PF9966/12
TV has started to show dark pink/purple pixels more and more often. They mostly show up after there has been something dark on the screen previously.
Screenshots: http/i.imgur.com/M9QcVMQ.jpg
http/i.imgur.com/Mdxf9JR.jpg
Screenshots were taken while the screen was paused. After unpausing, the dark spots that made up riders bodies were clearly seen for some time: http/i.imgur.com/t15PCCI.jpg

The dark pixels are not static (not a permanent burn-in) and can disappear or appear on different screens. Can this be fixed by adjusting the Vs or Va at the back panel? Is there any other way?

 

[radR]

Just an update in case anyone stumbles here with a similar problem:

I opened the back panel and adjusted the voltage (Va or Vs or whatever). It's been a long time, but it has worked ever since.