Sound like CloudFlare is blocking access to Master Server API, due to the SRB2MB server move
see https://git.do.srb2.org/STJr/SRB2/-/merge_requests/2226
In the next version of SRB2, if are are still using https://mb.srb2.org/MS/0, and it be changed to https://ds.ms.srb2.org/MS/0 for you, and...