This article explains the reason for new URL added to custom URL categories not being blocked by UTM
There are close to 52k blocked URL under 20 custom categories, after adding new URLs to custom categories and committing the configuration, the sites are allowed rather than blocked.
The sites are getting blocked after sometime without any action or after a empty commit.
This issue is due to large number of URL patterns, which causes the PFE control path memory exhaustion.
Due to this memory exhaustion the synchronization between RE and PFE.
Fix is added from junos:25.2R2 junos:25.4R1 onwards.