When a virtual machine is consuming almost all of its allocated memory without a significant change in workload, the first thing to investigate is memory leaks within the application. Memory leaks occur when an application improperly manages memory allocations, resulting in increasing memory usage that is not released back to the system for other tasks. This gradually reduces the available memory, leading to performance issues. Investigating for misconfigured cache is important but not the primary concern since it is not directly related to a sudden increase in memory usage without workload changes. Inadequate swap space can contribute to performance problems but is unlikely the sole cause if the application's memory consumption is consistently high. Insufficient physical memory would be an issue of resource allocation that should have been flagged before a new workload increase.