I'm using Version 7.16.44 (x64) on a Windows 10 machine. The only project I am running is Einstein@Home. Starting just last week, my system went to 100% memory usage. After reboots, it takes 15 minutes and it goes back to 100%. Checking task manager it shows BOINC using 97.5% of the memory.

I have had this system running BOINC for a year with no issues until now. I have 32GB memory installed. This system only runs BOINC and is used to store files on my network.

Any suggestions?

You didn't specify how many threads/tasks you are running simultaneously and how much RAM is available before BOINC starts. Not knowing that information, I will inform you that Einstein has been sending out some new type of work lately named:
Multi-Directional Gravitational Wave search on O3 (CPU) that needs around 2GB per task RAM and just about the same about of swap file also is needed.

The latest version of the BOINC client is 7.20.2. I suggest you download and upgrade to the latest version when you have time. There has been many important bug fixes since the version you are using.

Some projects have applications and tasks that will grab all the cores and all the memory you have, which can cause problems almost regardless of you computer.
A couple of things that will help, both can be done on the troublesome PC using BOINC's "advanced view"

First restrict the amount of memory tasks running under BOINC can use:
options>computing preferences>disk and memory
then reduce the % of memory when the computer is in use" to say 75%, and "when computer is not in use" to say 85%

Next, reduce the number of cores used by BOINC:
options>computing preferences>Computing
the set "use at most % of the CPU" to give you at least one free core - e.g. on a four core system setting to 75% give one spare core and three for BOINC to use.

Obviously you can vary the figures above to suit your needs and you computer.

Next, reduce the number of cores used by BOINC:
options>computing preferences>Computing
the set "use at most % of the CPU" to give you at least one free core - e.g. on a four core system setting to 75% give one spare core and three for BOINC to use.

This may not be needed with all applications but while I allow 95% of memory while computer not in use and 80% while in use, if I want to use the computer much when some types of task are running, I restrict BOINC to n-1 real cores where n is the number of real cores. Quite a lot of applications you get no increase in throughput by using hyperthreading.