After the upgrade to Osclass 8.2 with php 8.1 - I see a warning in the Apache log:
Undefined array key 0 in /home/u4*****/domains/domain.be/public_html/oc-includes/osclass/helpers/hDefines.php on line 800\n

Line 799 and 800 is:
     if(osc_subdomain_type() == 'category' && $cat[0]['s_slug'] != osc_subdomain_slug() || osc_subdomain_type() != 'category') {
     $category = $cat[0];
Adding an @ in $category = @$cat[0]; clears the warning message but does not solve the error. Any idea how to fix this correctly?

Well question is, how it is possible that your item category does not have hierarchy?
Anyway added small fix that will be in 8.2.1

No idea why the categories have no hierarchy. However, I use original files. In any case, it will be fine with v8.2.1, thank you