Dashboard Problems

Upgraded from 2.3 to 2.5, a few Dashboard pages seem to be OK, such as 'Roles & Permissions' and the forum itself seems OK too, although I can't get to the Plugins page to even try to enable jsConnect for SSO.

In fact most of the Dashboard sidebar and the top menu items default to the same page titled "Need More Help?" with a banner "We recommend using MySQL 5.6 or higher. Version 5.5.58-0+deb7u1-log will not support all upcoming Vanilla features."

The javascript console shows errors similar to the sample below for every Dashboard page:

[Error] Failed to load resource: the server responded with a status of 404 (HTTP/2.0 404) (vanillicon.woff, line 0)
[Error] Failed to load resource: the server responded with a status of 404 (HTTP/2.0 404) (vanillicon.ttf, line 0)
[Error] Failed to load resource: the server responded with a status of 404 (HTTP/2.0 404) (vanillicon.svg, line 0)
[Error] Failed to load resource: the server responded with a status of 404 (HTTP/2.0 404) (tooltip.js.map, line 0)
[Error] Failed to load resource: the server responded with a status of 404 (HTTP/2.0 404) (util.js.map, line 0)
[Error] Failed to load resource: the server responded with a status of 404 (HTTP/2.0 404) (collapse.js.map, line 0)
[Error] Failed to load resource: the server responded with a status of 404 (HTTP/2.0 404) (modal.js.map, line 0)
[Error] Failed to load resource: the server responded with a status of 404 (HTTP/2.0 404) (dropdown.js.map, line 0)

The site is hosted by 1&1 with:
Apache 2.2.22
PHP 7.1
MySQL 5.5.58-0+deb7u1-log

I have an option to upgrade to PHP 7.2, but I have no control over the MySQL version.

Any suggestions welcome, or is 2.5 a non-starter for me?

Thanks,
John