Up until like a year or two ago, YouTube links always used to be pretty clean. The format was youtube .com/watch?v=[video_ID]. A year or two ago, they started adding a tracking suffix on, so it would be youtube .com/watch?v=[video_ID] &si=[tracking_ID].

Over the last day or so, I've noticed links with a different format, youtube .com/watch?v=[video_ID]&pp=[tracking_ID] - only the pp= string is much longer than the si= string. This can only be because they're including more information in it. What that information is is anyone's guess.

This is basically a PSA to watch YouTube links more carefully, as people are by and large complacent with them (moreso than other links) and never even realised the si= change, let alone this new pp= change.

It could also be that the change to pp= is meant to circumvent communities, like this one, which automatically filter out the si= suffix. They may have decided to address that, then took the opportunity to make their tracking more severe.