Known problem, it happens when phone's time go ahead, automatic time do not help. I use ClockSynk to check this before every battle. Offset (in ClockSynk case) should be negative, otherwise you'll get an error.
So for raid purposes manual time works better, if time set to automatic system could change time spontaneously.
How to set time properly is another topic, without root apps do not allowed to change system time, but with root one could get issues with running pogo.
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Problems with OnePlus 3T on raids?
Any users of the OnePlus 3T have any problem on the raids getting an error message when starting the fight? I get error on random times, sometimes i can play normaly, sometimes I can't do the raid because of this and it's so annoying.
For example yesterday i did a Moltres raid succesfully and today did a Tyranitar and Moltres and on both I got error.
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