I wondering if anyone knew if Grand Slams and 1000s are not being treated as mandatory countable tournaments, as far as I was aware the grand slams and 1000s were counted regardless.
Not certain where you got that table from. It doesn't show Tsitsipas's points from AO2021 or RG2021 which are included in his official ranking (presumably scrolled off the top of the list)
On the ATP website under Rankings - FAQ there are several statements on how the rankings should work.
It states the following for 2021:-
"The breakdown - for singles and doubles will include 19 events for all players starting in 2021. *In singles, the Nitto ATP Finals is an extra event (20th) in the ranking breakdown. Top players who compete at all mandatory events will have the following breakdown:
One (1) Nitto ATP Finals* (additional event in the ranking breakdown)
Four (4) Grand Slams
Eight (8) mandatory Masters 1000s
Seven (7) Best Other (ATP Cup, ATP 500, ATP 250, Challenger, ITF)"
But there was an adjustment due to COVID
"In October 2020, due to ongoing COVID-19 concerns, ATP announced that it would move to a Best of 24-month ranking, extending the current ranking approach through and including the week of 1 March 2021. All events continue to be non-mandatory through this period"
The last setence explains the Paris and Wimbledon points.
It was taken from the ATP website under ranking breakdown for Tsitsipas, I couldnt get a screenshot showing all the tournaments. So its just a case that all tournaments were non mandatory up til August 2021 as per the ATP website.. In March, the ATP extended the Best Of logic for the ATP Rankings through to the week of 9 August 2021 (inclusive of Toronto). This would explain why Wimbledon isnt counted but unsure about Paris Masters then as it was after Aug 2021, unless all events are still non-mandatory?