Did you get below error when you try to start CSF.

Error: csf: Incorrect CONNLIMIT setting: [50], at line 2484

This error was comming  becuase CONNLIMIT=50 is not a valid setting for the latest cpanel version.

Syntax for the CONNLIMIT setting:

CONNLIMIT = “80;50” means:

Only allow up to 20 concurrent new connections to port 80 per IP address