unable to load images in phplist - need queries to help troubleshoot

Hello. I hope everyone is safe and healthy. I know that this forum is not for troubleshooting particular software. But bear with me. . . Suddenly images that normally load no problem in phplist are intermittently NOT loading. There seems to be no rhythm or reason. It is intermittent. To troubleshoot I would like a command(s) that would parce logs all of the failures or any recommended commands to help troubleshoot this. I am looking for commands for failures to load for specific requesting IP address to drill down into what piece of software on the server is denying the loading of images. Or any other recommended trouble-shooting methods. Thanks in advance and wishing everyone a calm and peaceful day.