Zabbix - Some options in frontend disappeared

[SDL_mine]

Hello,
I'm having an issue which prevent me to select or view some options: it happens on existing hosts, while creating a discovery rule, and I'm also getting following error while going in problems -> and selecting "show suppressed items" :

--------------------------------------------------------------------
Fatal error, please report to the Zabbix team

Controller: problem.view
action: problem.view
filter_application:
filter_evaltype: 0
filter_inventory: array
filter_name:
filter_set: 1
filter_show: 1
filter_show_opdata: 0
filter_show_suppressed: 1
filter_show_tags: 3
filter_show_timeline: 1
filter_tag_name_format: 0
filter_tag_priority:
filter_tags: array
--------------------------------------------------------------------

I've tried to do "apt-get install --reinstall zabbix-frontend-php zabbix-server-mysql" but didn't help.Can you help me?

I'm attaching some screenshot to help clarify the issue.
Thank you in advance,
Best regards

[SDL_mine]

Hello,
I have managed to workaround the issue: the problem seems to be our WAF. Disabling it, the frontend is working again. I'm writing this so that someone could benefit from the info.
thank you
BR

[vladimir_lv]

Hi!
What is your Zabbix version? Also, check the check php-fpm --version

[SDL_mine]

Hi,
Zabbix version is 5.0.24 and I ghave php-fpm 7.4.3 installed.
BR

[SDL_mine]

Hello,
I have managed to workaround the issue: the problem seems to be our WAF. Disabling it, the frontend is working again. I'm writing this so that someone could benefit from the info.
thank you
BR