New version of Joomla suggest to upgrade PHP to version 7.1 or higher for security reasons.
When I upgrade PHP to 7.1 or more, warning
Parameter 2 to modChrome_artnostyle() expected to be a reference, value given in … modules.php on line 36
appear on web page. I was looking for solution to hide this warning on internet, but there was no answer. It seems that Artister support is dead, so I start to investigate and find out where is the problem. Maybee this can help you to preserve web pages with Artisteer templates and keep it on last versions of Joomla and PHP.
First you need to find out which modules produce this warning. I realize that this warning comes from Custom HTML modules. So I open each Custom module, go to Advanced tab and change Module Style to System > none. Warning dissapear and site works fine. Same was with showplus slideshow module.
I suggest always try first with PHP 7.1, solve warnings and later rise PHP version.
When I change to PHP 7.3 some other PHP incompatibility occour so I need to change some PHP sorce files from continue to continue 2. I also need to set nd_mysqli parameter in PHP 7.3 and now everything is working.
Try and see. It works for me.