This article explain how to fix the logging issue of wincollect events after the upgrade to 7.5.0 UP4 and later

Managed WinCollect versions 7.3.1 p2 and later are compatible only with JSA 7.5.0 UP4 and later.

Managed WinCollect versions 7.3.1 p1 (build 22) and earlier are compatible only with JSA 7.5.0 update package 3 and earlier. Managed WinCollect 7.x users who want to update to JSA 7.5.0 UP4 must perform an sfs installation of JSA 7.3.1 p2.

Please refer to the document 'Installing and Upgrading the WinCollect Application on JSA Appliances' for performing an SFS installation of WinCollect in JSA.

Please download and install the file "WinCollectupdate 7.3.1-28" under Agents from the portal below:

https://support.juniper.net/support/downloads/?p=jsa-signatures