Tnx UFHH! It seems things went wrong during upgrade. This is what I find in the upgrade.log:
2016-02-23T00:32:32+01:00 [INFO] Your upgrade of Web Presence Builder to version 12.5.29 was completed successfully. No errors were encountered.
2016-02-23T00:32:33+01:00 [INFO] Starting the update of the "headers" resources...
2016-02-23T00:32:35+01:00 [INFO] Finished updating the "headers" resources.
2017-07-03T12:08:02+02:00 [EMERG] /sitebuilder/JsonApi/ SB_Upgrade_Exception: The database upgrade is not completed.
file: /usr/local/sb/include/SB/Upgrade.php
line: 386
code: 0 94.211.0.85
https://domeineiland.nl:8443/sitebuilder/Editor Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.115 Safari/537.36
2017-07-03T12:20:32+02:00 [EMERG] /sitebuilder/JsonApi/ SB_Upgrade_Exception: The database upgrade is not completed.
file: /usr/local/sb/include/SB/Upgrade.php
line: 386
code: 0 94.211.0.85
https://domeineiland.nl:8443/sitebuilder/Editor Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.115 Safari/537.36
2017-07-03T12:25:04+02:00 [EMERG] /sitebuilder/JsonApi/ SB_Upgrade_Exception: The database upgrade is not completed.
file: /usr/local/sb/include/SB/Upgrade.php
line: 386
code: 0 94.211.0.85
https://domeineiland.nl:8443/sitebuilder/Editor Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.115 Safari/537.36
2017-07-03T12:58:39+02:00 [EMERG] /sitebuilder/JsonApi/ SB_Upgrade_Exception: The database upgrade is not completed.
file: /usr/local/sb/include/SB/Upgrade.php
line: 386
code: 0 213.93.122.2
https://domeineiland.nl:8443/sitebuilder/Editor Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.115 Safari/537.36
2017-07-03T19:03:38+02:00 [EMERG] /sitebuilder/JsonApi/ SB_Upgrade_Exception: The database upgrade is not completed.
file: /usr/local/sb/include/SB/Upgrade.php
line: 386
code: 0 94.211.0.85
https://domeineiland.nl:8443/sitebuilder/Editor Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.115 Safari/537.36
2017-07-03T20:27:09+02:00 [EMERG] /sitebuilder/JsonApi/ SB_Upgrade_Exception: The database upgrade is not completed.
file: /usr/local/sb/include/SB/Upgrade.php
line: 386
code: 0 213.93.122.2
https://vps.domeineiland.nl:8443/sitebuilder/Editor Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.115 Safari/537.36
2017-07-03T20:38:13+02:00 [EMERG] /sitebuilder/JsonApi/ SB_Upgrade_Exception: The database upgrade is not completed.
file: /usr/local/sb/include/SB/Upgrade.php
line: 386
code: 0 213.93.122.2
https://vps.domeineiland.nl:8443/sitebuilder/Editor Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.115 Safari/537.36
Have you any idea how to repair this?
I already tried the plesk repair you suggested without the wished result.