PS5 Redsec matchmaking not working with Crossplay OFF

I am experiencing a matchmaking issue in Redsec mode on PlayStation 5 that started suddenly on December 18.

Platform: PlayStation 5
Mode: Redsec
Crossplay: OFF

Timeline:
Until December 18 around 01:00 (Asia time), matchmaking worked normally.

Asia server (no VPN): match found

North America West server (using VPN): match found

From around December 18 ~10:00 onward, matchmaking no longer works at all when Crossplay is OFF.

Reproduction steps:

PS5, Redsec, Crossplay ON
Result: Matchmaking works on Asia server

PS5, Redsec, Crossplay OFF, Asia server (no VPN)
Result: No matchmaking

PS5, Redsec, Crossplay OFF, North America West server (with VPN)
Result: No matchmaking

PS5, Redsec, Crossplay OFF, Europe server
Result: No matchmaking

Additional notes:

Network, NAT type, and console settings have not changed

Issue occurs regardless of VPN usage

The same setup worked normally until early morning on December 18

This appears to be a server-side matchmaking or backend change affecting PS5 Redsec queues when Crossplay is OFF

Please check if there was any backend or matchmaking logic change affecting PS5 players using Crossplay OFF in Redsec mode.