Went to check on it myself, "Oh damn, you're right..."
Replace the phone immediately under warranty and turn the brightness down. It's not a POS phone, all phones with our type screens do this. No brighter than 75% with sun contrast on. More then bright enough.
I don't notice it on mine but I always minimize the navbar in most cases and if i need to use it quickly bring it back up.
I also have my colour profile changed more towards the warm side. I use a greenish colour for my accent. Blue is probably the worst one to use as the oleds die quicker. I also usually keep my screen at 25% unless I am in bright areas where I let auto take care of it with the suggested setting. But I use my phone constantly. If I use continuum I use a black 1440x2560 image I saved and open it in photos in full screen mode. My timeout is also set to 3 minutes. I use dark theme as it's much better for oled.
And it may not be ghosting you notice if you see it slightly after moving it down. That is just refresh rate delay in some cases. If you truly want to see get a 1440x2560 pure white image and open it full screen in photos.
I have been using my dual sim 950 xl for about 10days now. I use full brightness all the time. I have checked my screen on full blown pure white image but can't see anything yet.
Will this issue definitely crop up?
I have been using my phone since May. I keep my phone on auto brightness (slider shows 25%), Glance always set to ON and I haven't seen any burning on the screen. It could be because I have the brightness set to low?
Follow Krystianpants' suggestions (or similar), and you should be fine for a long while.
I would go exchange it right away.
In all honesty it shouldn't happen that quickly even with bad use. My bro has a 925 for almost two years and still no burn-in. He doesn't really take care of it much either. Could be the oleds were just faulty. I do everything to keep it running long but there's a certain level of quality you need to expect from a flagship.
The complete starts from day you buy it. I got 2 years.
You can exchange it under regular warranty. But they may take it back and try to fix it by changing the screen. Under complete you have the option of getting a completely new phone right at the MS store for a deposit. I bought the warranty before they changed the pricing so I pay 25 bucks and they give me a new phone, no matter what happened. I could drop it and break the screen I pay 25. If you bought it after the price change you will pay 50 bucks. The 2 year gives me 2 complete exchanges. So I can break it twice and get a brand new phone. So Talk to them and find out what they will be doing to fix it. If you have the complete and it's near it's ending It would probably be better to take the new phone option.
I can confirm that I can now see faint traces of the live tiles on a a white background too, but only if I look very carefully. I will try to take a pic with my DSLR later.