OK,
Here are my symptoms, pretty similar:
Key (or better remote) started to work spotty
Sometimes it worked then it didn't
Then my first key fob stopped working altogether.
Used the 2nd key and this one started to like 6 months later.
The red lights flashes slower or not at all.
Of course I replaced the batteries etc.
At the end I bit the bullet and got one new key fob from Porsche for around $250
and that took care of all the problems. Seems like the key fobs have a limited life span. In my case it was 8 years...