In general the Windows CE operating system used by PV+ loads the whole OS and application into RAM at startup and only uses the SD card or actual hardware file system for log files. Abandoned *.MER files or overflowing log files would not affect the runtime.
It's technically possible for the runtime to have a "memory leak" or for the split of RAM allocation between Storage Memory and Program Memory might be insufficient for your runtime needs. Typically you will see a Windows CE "Out of Memory" error if that happens.
Most FTView ME applications don't run out of memory, but large ones with complex screens can, especially if you use a lot of "on top" displays instead of "replace" displays.
If this were my system I would create a diagnostic screen that has the FactoryTalk Diagnostic list object on it, and maybe some numeric display fields showing some of the pre-defined System variables related to memory.
That will let you see if there are persistent configuration-related comms problems (like it's trying to read non-existent tags from the PLC), or occasional timeouts that might be related to a physical network problem, or a resource problem on the PLC side.
Edit: Welcome to the PLCTalk forum community !
While I don't reflexively say "upgrade the firmware !", if your PV+ is more than 10 years old or running pre-v5.10 firmware, you might get performance and stability benefits from a firmware upgrade. Check the part number and firmware versions on the sticker on the back, and/or the actual firmware version shown on the configuration screens.