Per ISU's Grand Prix Designation of Skaters:
1. Seeded Skaters (#1-6 at Worlds) will be assigned 2 spots.
Alina & Zhenya each get 2 spots
2. Invited Skaters (#7-13 at Worlds) will be guaranteed to be selected for 2 spots.
Sofia gets 2 spots
3. Invited Skaters with ISU World Standing Top 24 and ISU Season Bests Top 24 (who aren't already in WS Top 24) will be guaranteed 1 spot. This excludes seeded and invited skaters above.
Guaranteed 1 spot: Maria (WS #9), Stasya (WS #13), Liza (WS #16), Sasha (WS #24); Shcherbakova (SB #9), Kostornaia (SB #11), Serafima (SB #18), Tarusina (SB #20, but stayed Junior), Gubanova (SB #21), Kanysheva (SB #22, but stayed Junior)
4. Invited Skaters who were medallists at Junior Worlds, or the gold medallist at Junior GPF will be included in the selection process. Note that the rule says included, and not guaranteed.
Included: Sasha (Worlds), Shcherbakova (Worlds), Kostornaia (GPF)
From my understanding, Feds are mandated to select from the seeded skaters (Worlds #1-6), then the invited skaters (Worlds #7-12), then the remaining invited skaters (WS & SB Top 24). Only after all those skaters have been invited to their guaranteed spots, can they move onto the general pool (Junior Worlds Medallists, JGPF Gold, Season Best Top 75).
Sasha gets her 2nd spot (JWGM), Shcherbakova gets her 2nd spot (JWSM), Kostornaia gets her 2nd spot (JGPFGM). Then, Liza gets her 2nd spot (SB #2). And I'm assuming RusFed selected Stasya as the host spot for her 2nd spot, although her SB #23 was enough for a 2nd spot.
After all aforementioned skaters have been invited in that order, feds are then supposed to confirm if the invited skater will participate in the GP.
Therefore, Gubanova was mandated to be selected for a 1st spot before a 2nd spot could be given to anyone but Alina/Zhenya/Sofia. I'm guessing RusFed decided not to confirm her selection.
Disclaimer that I do not think Maria should have been denied her GP spot. I'm just confused when people state her World Standing (WS) as the reason why she deserved the spot over others. While it's true that her WS earned her a guaranteed spot, we should remember that Gubanova's Season Bests (SB) also guaranteed her a spot. ISU did not state that WS takes precedence over SB.
If we argue that Maria earned her guaranteed spot, then we must also say Gubanova earned her guaranteed spot. Since she was not given her earned guaranteed spot, RusFed effectively chose Maria over Gubanova - which then somewhat legitimizes the question as to why Maria deserved it more than Gubanova?