The 7★ Guaranteed (Re)summon issue has been resolved in version 3.8.9 released on 12/19 PST.
Players who were unable to continue with their re(summon)(s) will be receiving 7★ Guaranteed (Re)summon [Compensation] Ticket(s), regardless of whether they have applied for a refund from their corresponding app stores.
The compensation tickets will be sent during maintenance on 1/29 PST and players will be able to use their compensation ticket(s) on the corresponding 7★ Guaranteed (Re)summon banners, which will be made available again after maintenance.
End of maintenance, Thursday, 1/30 - Start of maintenance, Wednesday, 2/5 PST
* Only certain units added to the game prior to November 21, 2019 will be included in the summon pools.
** Limited time and collaboration units are not included in the summon pools.