Broken themes in 2.1.10
I'm working on an older forum, v2.1.10 (I'm working a plan to upgrade to 3.x) but recently an incident occurred that seems to have broken most themes. The default theme works but none of the others do, as well as none of the mobile themes, it just produces a blank screen. I suspect something is wrong with Smarty but need some help diagnosing the issue.
The cause of the problem was a security incident on the server which required me to restore a backup of the vanilla files. I simply overwrote what was there with a backup from a few days earlier. Everything else works except for some themes.
I've verified there's a /cache/Smarty/cache folder and a /cache/Smarty/compile folder, both have the correct permissions. I'm at a loss, does anyone have some ideas for me?
You shouldn't waste time and energy in recreating that old forum. You have had a security issue and you will get the next. By the way: this is not only "your" security issue. You expose the data of all of your users - not what I would expect from the admin of my forum.
That installation is so old that it cannot be guaranteed that it is working with current PHP versions. Really, simply do an update. It's not that hard...
That said, you still might want to have an answer to your question. Try deleting the files in the cache folders. A blank screen is a hint for a PHP error. You will find more information on the reason for your problems when you take a look at your forums error log files