This error occurs when WordPress or a caching plugin attempts to rebuild the cache but runs out of allocated PHP memory. This happens primarily when the PHP configuration’s memory_limit is too low to handle the memory demands of rebuilding the cache, especially for large sites with extensive content or complex data structures.
The memory exhaustion can be triggered by large databases, inefficient cache rebuild logic, resource-intensive plugins, or server-level limitations that terminate the process prematurely during long cache rebuilds.