Here's the email I got from Pia. Hope this helps clear things up. Basically we'll be let in in the order of our ticket numbers at Gate W for standing. Here's the email in full:
Behalf of U2 Joshua Tree Tour 2019 - We would like to welcome you to Saitama Super Arena.Due to recent events, extra security measures will be in place, with inspection of bags and metal detector body checks conducted upon entry.As a result, entry to the venue may take longer than usual, so we encourage you to arrive with plenty of time to spare.Certain items are prohibited from being brought into the venue, so please carefully check the official site at https://www.u2japan2019.com/We appreciate your co-operation and understanding.■Standing (Front/Rear) ticket holdersPlease enter the venue via W Gate.Entrance will be conducted in the order of the number indicated on your ticket. A stand-by area for entry will be opened one hour prior to doors.Please ensure that you follow instructions of staff, and enter the venue in the order specified.A cloakroom will be available. The counter will open from 1pm, with a charge of ￥1,000 (one bag, up to 45l).After checking your bag in, it will not be possible to check it out and in again. The cloakroom will be located by Gate S2 (1st floor), within the Saitama Super Arena Exhibition Hall.The cloakroom is unable to take custody of high value items and will be not held liable for any theft of such. Please ensure you take responsibility for your own belongings.With the exception of unopened plastic bottled water, food & drink may not be brought into the Standing areas.■ SS seat ticket holders Please enter the venue via A Gate. The SS ticket holder gift will be distributed upon entry.Please note that SS ticket gifts will not be distributed at a later date for those who are unable to attend the concert.With the exception of unopened plastic bottled water, food & drink may not be brought into the SS seated areas.■ S seat ticket holdersPlease enter the venue via N Gate.■ A seat ticket holders Please enter the venue via N Gate.■ Stage Side seat, Back Stand seat ticket holdersTicket holders with seats located on 200 level should enter via A Gate.Certain items are prohibited from being brought into the venue, so please carefully check the official site at https://www.u2japan2019.com/before traveling to the event venue.
Hope that helps!