HS 4.4.5 + PHP 8.x gives registration "error"

-- HikaShop version -- : 4.4.5
-- Joomla version -- : 3.10.4
-- PHP version -- : 7.4.27/8.0.14
-- Error-message(debug-mod must be tuned on) -- : #0 implode(): Argument #1 ($pieces) must be of type array, string given

When combining hikashop 4.4.5 with PHP 8.x(0.14 in my case) registration partially fails. On the front-end the error

"#0 implode(): Argument #1 ($pieces) must be of type array, string given" is shown, implying to the user that there was a problem (i don't know what) registering. However when checking on the BACKEND, the user is listed. When setting PHP back to 7.4 everything functions as normal.

Seeing as PHP 7.4 has entered its security release only, it's vital for me to move all my sites over to PHP 8

Sorry about the delay. Forum didn't notify me of a response despite enabling the option.

on the front-end, nothing changes. Error remains identical. Pressing the browser "back" button (not using a standard page refresh) the warning "You must accept the privacy policy" appears. Could this be another "GDPR" induced problem?

Trying to edit a user on the backend though gives the exact same error.

0 implode(): Argument #1 ($pieces) must be of type array, string given.

Trying to modify an existing user on the backend gives the same error, but the change IS saved.

Setting error reporting on the backend to "development" gives the following error.

Warning: Trying to access array offset on value of type null in /var/www/vhosts/<domain.tld>/httpdocs/administrator/templates/isis/html/com_users/users/default.php on line 96

Go back to 7.4 and the backend warning stays but front-end registration behaves just fine and an activation link is e-mailed. Based upon the e-mail look and the link sent it has to be something hikashop related i think. As the link that gets sent is

/index.php?option=com_hikashop&ctrl=user&task=activate&activation=<insert hash?>

below the link the username that just registered gets listed.

So i asked this question over at the Joomla forum too. A mod had this to say (see attachment). Maybe it's of help, as the only extension i know of that is installed that modifies user registration is the hikashop registration redirect plugin.

additional info

i checked out that specific file just now and its this

$allowed_admins_prm_arr[] = $allowed_admins_prm[0]

Then out of shere curiousity i figured lets check the header if this is even a hikashop file at all. It's not. Its from the component "Login As User" by Web357. I need to take this issue up with them. I'll let you know how this turns out