You might have a leak in the air ride. Spray some soapy water on top of the air spring, diaphragm, or the air lines while keeping an eye out for bubbling. Also, check the solenoid valve that's inserted into the air-spring.
One of my other Marks(BA) used to behave the exact same way while maintaining ride-height but would struggle to pick itself up after highway speeds. I could hear a "hiss" every now & then from the front driver's side and would sometimes find the front of the Mark a bit lower than usual or fully slammed after being parked for long periods.
So, I ended up getting a WESTAR replacement air-spring. When I removed the solenoid from the failing air-spring I noticed the top black cap(where the air vents from) had broken and was stuck inside the solenoid cavity.
View attachment 828571493
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Both solenoids in the pictures are from FORD.