I found an explanation of this on twitter which sounds reasonable and maybe explains the vagary. I don't know, but I'll just paste here anyways:

Twitter's rate limiting is not what everyone is thinking it is. It is not to punish non-paying users.

"Data scraping" is a big deal. This is where automated systems load the website or app and pull your tweets/data. It's a huge security issue. Automated systems are pulling every tweet/word/user account information to store in an unknown database somewhere else.

This could be state actors like China, the US Government, Australia, or other bad political actors like PAC's that are trying to gain access to everyone's information to analyze and use for nefarious things. Manipulating what is said on the site can be done at scale with data scrapping.

It could also be used to figure out the identity of Anons or to punish people in their country for what they tweet. Looking at you #Australia and #Canada and #UnitedKingdom

The temporary measures of limiting tweets is to protect users just as much as it is to protect the entire Twitter network from going down. They are currently scrambling to get ahead of this and tune their network security to block it from happening again.

It's also important to note that twitter has 500,000+ servers. That's not free. In cloud data centers, the companies that use them have to pay for what is called "ingress and egress" of data going "in and out" of the servers. A data scrapping event that is large enough for them to start limiting means that it was a MASSIVE event that could be considered an attack on the site.

[interupting the quote to point out a massive spike in TOR clients in various European countries recently, could be related:

https://news.ycombinator.com/item?id=36560136]

It would also put massive load on their servers and cost them so much money it could threaten the site's financial ability to keep running. It could be on purpose to put twitter out of business from cost alone.

Many people are misunderstanding why @elonmusk wants people to pay for twitter or for the twitter API (a programming interface that can pull data for other sites and apps).

The reason he wants people to pay is because if China or porn companies want to create massive bot farms of fake accounts, it is currently free. These bad actors are highly skilled and operate like a business. They have professional staff that continuously change their tactics and Twitter engineers have to fight 24/7 to stay ahead of them. If they have to pay for every account or pay to use the API, it would cost them A LOT of money. This limits the amount of people who could create bots, put automated porn on here, and the hacking/scrapping/DDOS attacks on the site. It protects you.

It also guarantees twitter will continue to exist without bloating it with tons of ads. This is all a part of the plan to create a free-speech place we can enjoy without being controlled by outside actors or advertising companies. I know $8 is a lot to some people but, it is for many reasons. None of the reasons are to hurt or punish people.

Here's the users twitter profile:

https://twitter.com/misteryrobozo