wew671 Hi
Having replicated the same on local install with PHP 7.1 however the template appears fine. Please provide us with the site url along with admin details in edit fields for troubleshooting purposes
For reference, You can follow thread post (5 point) procedure.
(Note - Kindly change the PHP version to 7x so as to troubleshoot the relative issue as mentioned and have the PHP version update stay for sometime when the issue is being investigated)
Also, As seen earlier with other simultaneous forum posts with similar issue, 3rd party extensions have also been the culprit resulting in such error so would also suggest to disable 3rd party extensions one by one