Petter Gisslen

https://sessionserver.mojang.com/session/minecraft/profile/lookup/bulk/byname does not exist and AFAIK never had, I think you did a copy/paste mistake.

Wiki is correct, you can use both URL for bulk lookup.

https://api.minecraftservices.com/minecraft/profile/lookup/bulk/byname

https://api.mojang.com/profiles/minecraft

We have problems with unintentional rate limiting, we are working on a fix for this. 

This is a know problem and we are working on a fix for it.

The old lookup URL is still active and is: POST https://api.mojang.com/profiles/minecraft

The fix is out in production, now it's 30 seconds 

We have added a 60 second cache on the profile lookup response ,so that is probably the reason. I think we can lower that to 30 secs if that will make your life easier.

Hi

We have enabled ip validation quite recently. This means that if the server has IP validation turned on(only a 5-10% of public server has) it will provide the public IP of the connecting client in the hasJoined request and the sessionserver will compare it with the public IP of the Join request. It the IP's does not match, we reject the hasJoined request (204)

If public IP och both server and client are the same we consider it on the same LAN and accept that also.