I am trying to receive player profile data via https://sessionserver.mojang.com/session/minecraft/profile/ .

Up until very recently, there was a limit only on duplicate requests, i.e., you could request the profile for the same UUID only so often per minute. However, you could post an unlimited amount of unique requests, which may be necessary in case a server has many players.

I cannot pinpoint since when that changed, but right now, it appears that even unique requests are limited to about 10 per minute before the API returns HTTP code 429 (too many requests).

I am filing a bug report because this is a heavy and, to the best of my knowledge, unannounced change. I noticed that the contents of the (base64 encoded) texture objects was recently changed, and I presume that this new limit was introduced as an unwanted byproduct.