Digging a bit deeper
Doesn't seem likely, for two reasons.
The pump is constant displacement. Restriction would make pressure rise, but flow in gallons per minute would remain about the same. That said, it won't rise much; if the filter element is or becomes restrictive, the filter bypass will open at something like 15 psi deltaP.
Well Dan I must thank you for posting your response.
In an effort to fully understand what the cause could be.
The factory Lyc. filter housing does have a bypass that would open and allow excess flow if the filter can intake holes did not have sufficient cross section to handle the pump output. However.....
On the R22 a B&C specialties STC'd 90 degree filter adapter is used. I had to look at a lot of photos and could not see a bypass. So then I downloaded B&C's continuing certificate of airworthiness - as STC'd equipment almost always have.
http://https://bandc.com/wp-content/uploads/2018/05/ica-bc700.pdf
"The OFA (Oil Filter Adapter) is engraved with the words “USE ONLY CHAMPION PN CH48108 OR PN CH 48109". These filters not only meet the dimensional requirements of the OFA but also provide the required oil filter bypass valve. The OFA does not provide this bypass valve. Use of a filter without a bypass valve could result in loss of oil pressure or engine lubricating oil if the filter becomes partially or completely blocked."
On a Robinson R22 the mount is located in a very tight and out of sight location.
I have not yet found an older 4 hole tempest filter to measure the hole dia. and calculate total cross section area, but the flow had to be slightly marginal and no doubt loaded the pump drive. The engine made 200 over TBO and was remanufactured and is back in service with only Champion filters since.
I have not studied or gone looking for the Homebuilt models of B&C filter adapters, but I suspect they also might not have a pressure relief built in.
EDIT : I just checked B&C's homebuilt Oil Filter Adapter info and the same certificate with instructions indicates there is no internal bypass in the Homebuilt OFA's either.
It is amazing what you find for details when you go looking.