I try the 1click upgrade (with the last module v3.0.3) from 22.214.171.124 to 126.96.36.199
[Ajax / Server Error for action upgradeDb] textStatus: "error " errorThrown:"Internal Server Error " jqXHR: " "
Then, when I try to open the back-office, I have a 500 error. When I enable PS_MODE_DEV I don't have it anymore, and I can see I am well in 188.8.131.52 in BO.
PHP info here: http://presta1and1.com/prestashop_184.108.40.206/info.php
If I try an upgrade on the same server from 220.127.116.11 to 18.104.22.168, no issue.