The memory usage of processes in any modern OS is not a fixed quantity but is in fact highly dynamic. At any given time the usage of a process will depend on how much RAM is in the system, what the process is doing now, what it was doing in the past, what other processes are doing now, what they were doing in the past, and more. All of these factors interact in very complex ways. Also, most AV products have multiple processes. For some products this is obvious, in others it is not. Finally (all I will mention, not all there is) the memory usage column shown by default in Task Manager (Private working set) does not show the full usage of a process. Actual usage can be substantially higher than shown. This is due to a misinterpretation of what the numbers mean.

It is not the process itself but the system memory manager that determines how much memory a process will have at any given time. The goal is always to maximize overall system performance, not to minimize memory usage. It usually does a very good job, far better than you could hope to do yourself.

Even in the same computer the memory usage of a process can easily vary by a factor of 10, and in some cases much more. I have seen this on multiple occasions. And none of this in any way indicates that anything is wrong.

I trust that the implications of this are clear.