Unfortunately they were not pingable anymore.
I just used this solution below and it worked.
The Shellies that had issues still showed Firmware 20201128-102046/v1.9.2 my Shelly that worked was already on v1.10.1.
I now upgraded all to v1.10.1 and see what happens.
Could be that they got stuck during firmware upgrade?...
My Solution:
(1) Disconnect the power from the Shelly by turning off a breaker or other means.
(2) Restore power.
(3) Within the first minute, toggle a switch connected to the "SW" input on the Shelly 5 times on/off (10 total) or press and release momentary button 5 times.