monitoring -> graphs, if host & group are set to "all", errors appear.
it seems to be caused by some graphs in a specific group, although it is not clear which one yet
preg_match_all(): Compilation failed: unrecognized character after (?< at offset 3 [charts.php:82 ? CPageFilter->__construct() ? CPageFilter->_initGraphs() ? CAPIObject->get() ? CAPIObject->__call() ? czbxrpc::call() ? czbxrpc::callAPI() ? call_user_func() ? CGraph->get() ? CMacrosResolverHelper::resolveGraphNameByIds() ? CMacrosResolver->resolve() ? CMacrosResolver->resolveGraph() ? CMacrosResolver->resolveGraphsFunctionalItemMacros() ? preg_match_all() in include/classes/macros/CMacrosResolver.php:590]