Problem with opencart extension not working when switching from php5.6 to php7.2

We're using opencart 2.0.3.1. So we have a problem with an options extension, it's called Option Combinations. The problem is the product pages can't be displayed and the options created by the extension disappear when we switch the site over to php7. We get an error 500 on the product pages and to get the products to display again you have to go to line 63 of [login to view URL] under /system/modification/catalog/model/catalog and change the line from "$otp_option_data[] = array(" to "$otp_option_data = array(" After this edit the products display fine, but the options created by the extension aren't being displayed. If I enable display errors it displays the same error over and over where the options should be, "PHP Warning: Illegal string offset 'type' in /usr/www/users/xucozurjmj/system/modification/catalog/view/theme/journal2/template/product/[login to view URL] on line 351" And I don't know what to do to fix it. The option combinations extension is a vqmod xml file. Is the problem with the extension using code not supported in php7, or is it a problem with the journal theme or opencart itself? The latest version of the extension doesn't support our opencart version and our support for it has run out. The only thing being suggested by my colleague is to update the whole opencart installation to a version that the newer version of the extension supports, but coming from experience having done this before, it sucks. Updating opencart is going to cause way more unnecessary problems with a bunch of other things, and seems overly complicated to maybe fix a problem with one extension as the extension has been taken over by new developers, so I'm not even sure if the options set up in our version of the extension would carry over to the new version of the extension. So basically we need this extension to work on php7. We'll provide the xml vqmod for testing on opencart 2.0.3.1 running on php7 as we can't give away ftp details to the actual website.