Dynamic blocks not rendering

[deodigital]

Hi there, I've been searching through issues and trying to find a solution to this, and tried loads of fixes but I'm just not getting any results so here goes...

Magento ver. 1.9.2.4, Lesti 1.4.9

Basically none of the Dynamic blocks are rendering anything to the page. If I remove them from dynamic blocks they render, but as expected remain there until the cache is cleared. Add them back in to dynamic blocks, clear the cache and they simply disappear. There are no errors in the logs, or on the page. Merge Javascript files is off.

I've got this working on a different server with the same version of Magento.

Which leads me to think it might be a PHP setting or some functionality that needs to be installed on the server, but I've been through the PHP config (5.6 and also tried it with 7.0) and can't see anything glaringly obvious.

Are there any particular PHP packages that need to be installed? I'm tearing my hair out because I can't see any errors, but it's not doing what it should...