The Availability report filter is reset when moving to 2nd page of results, so "Template trigger" gets set to "all" which shows all the items from the Template chosen and you end up with lots of pages.

I was able to reproduce with version 2.4.6 and this is probably applicable to other Template triggers.

How-to reproduce
1. Goto Availability report
2. Choose:
Template group:all
Template: template os linux
Template trigger: zabbix agent on hostname is unreachable for X minutes
3. Press Filter
4. After page 1 is displayed, choose page 2. (you need to have more than 50 hosts for this to work)