Can you also, please, note values for the following settings:
1) Administration -> General -> GUI: Limit for search and filter results
2) User settings -> Rows per page

Normally resetting filter in host list should not overload the frontend.
It could be useful if you could enable debug mode and show the summary data for page (top 5 rows of profiler) and list heaviest SQL's if any.

1) Was set to 5000 (verifying during host import), I did crank that down to match user settings....

2) 500

Those settings were persistent in the 4.4 configuration btw (5000, 500 respectively) without HTTP 500 error - I will need to work on a maintenance window to get debug (is there a level preference in server conf)? We had just moved the server into production.......

Sorry, I misunderstood, which page you are talking about.

This can be a problem from ZBX-18071. You can try to apply the patch from that task to check, if it will help.

I attempted the patch - there is no change. Seems that issue relates to even getting latest data to load, mine relates to trying to clear/reset it to blank/no filters. I don't have any SQL queries hanging, nor do I get any debug messages in the UI. Just the memory error in nginx. Also we are using mariadb on the backend versus postresgl.

My work around it to go to Monitoring->Hosts to load latest data ILO clearing and picking new filters.

nginx error:

2020/08/06 15:35:55 [error] 6261#6261: *213 FastCGI sent in stderr: "PHP message: PHP Fatal error:  Allowed memory size of 134217728 bytes exhausted (tried to allocate 20480 bytes) in /usr/share/zabbix/include/db.inc.php on line 397" while reading response header from upstream, client: 10.218.4.120, server: FQDN, request: "GET /zabbix.php?action=latest.view&filter_rst=1 HTTP/1.1", upstream: "fastcgi://unix:/run/php/php7.2-fpm.sock:", host: "FQDN", referrer: "https://FQDN/zabbix.php?action=latest.view&filter_hostids%5B%5D=9805&filter_hostids%5B%5D=9808&filter_hostids%5B%5D=9809&filter_hostids%5B%5D=9816&filter_hostids%5B%5D=9817&filter_hostids%5B%5D=9818&filter_application=Disk+Partitions&filter_select=&filter_set=1"

latest view by filter or host does not seem to matter, same error even on lightly monitored hosts (less than 200 items). When I push memory to 1G the page will load but loads all hosts ILO clearing all hosts. Added screenshots of latest view, then after reload when memory pushed to 1G

Debug:

Total time: 0.022654
Total SQL time: 0.047475
SQL count: 39 (selects: 34 | executes: 14)
Peak memory usage: 4M
Memory limit: 1G

Thank you for your help. We will be looking into it.

Closing as duplicate of ZBX-18071.