It's filtered by one of the default/out-of-the-box filters. See it at RME - Tools - Syslog - Message Filters:
Name: Link Up/Down Message Filter
Type: Message Filter
State: Enabled
Devices_Latest: *
Messages: LINK-*-3-UPDOWN:* LINEPROTO-*-5-UPDOWN:* LINK-*-5-CHANGED:* LINK-*-5-UPDOWN:*