Question Error message after updating to 5.1

I cannot just ignore this problem.

As you suggested, tried to switch to Protostar template, but I deleted this template before, for some reason I cannot reinstall it. So I downloaded a different template, Sunny Blue Template, from joomla.com and switched to it. I still get the same error message.

Screenshot attached.

Thanks, Petrovanovich, for sharing. After you deleted all Kunena menu and menu items, where did you restore them? I do not see restore field on Kunena tool page.

backend - kunena - tools - menu manager- restore kunena menu

The only thing you need to do then, is to enable the forum menu item on your main menu.

velieb wrote: Thanks, Petrovanovich, for sharing. After you deleted all Kunena menu and menu items, where did you restore them? I do not see restore field on Kunena tool page.

I wanted to add a screenshot, but only a quick form of comments worked.

Here is a doc, where you can see the right way for customized Kunena menu items.
docs.kunena.org/en/faq/custom-menu-items

Thank you all for the help!
It seems that I need to wipe out all menu related items and category page custom urls... and rebuild entire Kunena pages in order to Kunena menu works. I hope this does not affect the page rankings, wish there was other way to solve it.

if you use the same aliases then you are ok, but this will just improve your page rankings

velieb wrote: It seems that I need to wipe out all menu related items and category page custom urls... and rebuild entire Kunena pages in order to Kunena menu works. I hope this does not affect the page rankings, wish there was other way to solve it.

I first wrote down to myself all the aliases of the puns of the Kunena menu. I too, was afraid of losing the structure of the aliases.
Then he deleted all these items.
After the restore, I returned the aliases back.
Two days could not decide, but everything went quickly.

Thank You, Petrivanovich.

I think I fixed the operand types issue. I can't reproduce the issue, so please check the nightly build.