isotope 2.5.5 - error msg / won't allow multiple products

I recently updated to isotope 2.5.5 (using contao 3.5.3) and keep getting error message whenever I add more than one product to my list. As long as I have one product per type in my store, all shop pages work and the form process goes smoothly; orders are recorded on the backend and test emails are sent and received. However, as soon as only one additional product is added (which is necessary) the product list page stops functioning and I get an error message. Help !

Note: I tried twice to copy and paste the error message from my systems log here but this post kept shutting down so I'm trying again without it. Hard to explain what's going on without the error log since I'm sure it has important details that would explain what's actually happening.

Yeah, the English forum is not in a good state.

Post the error message to pastebin and then post the link to pastebin here.