Same here for PHP 7.1. I run three separate sites using t3 on my server; one succeeded doing the upgrade to 2.7.4 and the other two give the error mentioned in the other posts (Error occur when upgrading. Upgrade failure). Is there any way to find out where the upgrade fails? A log file or something? The I can share it here to help pinpoint the error. What I noticed is that both sites that fail have a few changes in the files, but none with conflicts (only C and U in the compare), so theoretically the update should work, as it has worked for one other site on the same system.