Forum "Fatal error: Out of memory" errors since moving from single server to cluster
 

I've had vB4 running for months without this issue on a single dedicated server. About a week ago we moved to a 3 server cluster (2 web nodes, 1 DB). We've done this temporary move for about 4 years now (we need the cluster during the 4th quarter of each year), so it's nothing new.

Ever since the move, everyone on the forum is seeing random "out of memory" errors when doing the most simple of forum tasks.

Here are some of the messages I've received myself and the actions that caused them:

Hard-deleting a post: Fatal error: Out of memory (allocated 4980736) (tried to allocate 7680 bytes) in /home/deals/public_html/forums/includes/class_dm_forum.php(123) : eval()'d code on line 1

Viewing a thread: Out of memory (allocated 4718592) (tried to allocate 491520 bytes) in /home/deals/public_html/forums/includes/class_core.php(4078) : eval()'d code on line 414

Viewing another thread: Fatal error: Out of memory (allocated 4718592) (tried to allocate 491520 bytes) in /home/deals/public_html/forums/includes/class_core.php(4078) : eval()'d code on line 422

Quick-replying to a thread: Out of memory (allocated 4718592) (tried to allocate 491520 bytes) in /home/deals/public_html/forums/includes/class_core.php(4078) : eval()'d code on line 414

Disabling a product: Fatal error: Out of memory (allocated 3670016) (tried to allocate 122880 bytes) in /home/deals/public_html/forums/includes/block/cmsarticles.php on line 206


Things I have done to try and fix the issue with zero success:

- had server provider increase PHP memory limit
- disabled plugin system
- used a clean template
- replaced forum files with new versions

Any idea what could be causing this?