As expected, more good information from ATADistance:

JR East Suica System Downtime Notice by Joel Breckinridge Bassett:

Mobile Suica maintenance is a regular nightly occurrence from 1am~4am with longer once a month sessions. The July 6~7 and July 20~21 Suica system maintenance work is very unusual for both the time, 9pm~5am on each night, and the reach: both Mobile Suica and JR East station Suica ticket machine services are going offline.
During the offline period you can still use plastic Suica and Apple Pay Suica for transit and purchases as usual, but Apple Pay Suica Recharge will be limited to cash only from 1am~4am. Remember that you can always cash recharge Apple Pay Suica at any convenience store cash register or 7-Eleven ATM machine.
All other operations such as adding Suica to Wallet and all Suica App functions, and corresponding services at JR East station Suica ticket machines, will be offline for the entire maintenance window.
This is heavy system work that JR East is doing in preparation for the new eTicketing system due next April. JR East already had one system meltdown last month. Let’s hope they don’t have another.

Be forewarned.