Welcome to the club. What club might that be, you ask? The “I ruined my spool because if 50°C is good, then 85°C must be better, right?” club. 
It happens to the best of us. This was a PETG filament. The spool however was the same one they used for PLA… OOPS!!! Bambu high temp filaments come on High Temp Spools BTW.
What you will want to note is any warning on the spool itself. Sometimes, the manufacturer will state what the spool is capable of in terms of max temps. It’s all too easy to mistakenly dial in the incorrect temp.
But from what you’re saying, your temp at 50c should have been more than adequate. So here’s the next tidbit I’d offer. “DO NOT TRUST THE DRYER”. You’ll want to verify for yourself what the actually temp is. For that you want a hygrometer/thermometer with an external probe. Why external? Because LCD displays turn black at 50c and are permanently destroyed at hotter temps. The external probe ensure that the device outside will remain at the correct temp.
This is the one I use because it has max temp of 70c. The box of three Thermometers also allows you to measure temps at different spots in the dryer.
As an example, I did a review on a Sunlu S2 and it was horribly uneven in temps. I would not have known this had I not had 3 sensors, one at the top, one inside the spool hub and one near the bottom. The temperature gradient was huge.
BTW: Here is the wiki that has the recommended drying times and temps, just in case you didn’t see it before.
https://wiki.bambulab.com/en/filament-acc/filament/dry-filament