I agree with the suggestion about removing the plunge spring when the unit is inverted, if the router weighs 17 pounds, the rise and fall components (everything except the the base and columns, would be in the order of 14 pounds, so to provide positive lift at the end of a cut the springs would be rated at around 20 pound.
Inverted this means that the raising mechanism has to cope with about 20 lbs from the spring and 14 pounds from the rise and fall components, so is working much harder. Without the spring, the unit should be easier to raise than it would be to plunge operating upright with the spring.
There should be a plunge lock at the column somewhere near the handles to lock the height when plunging. Use it to lock the height once you have adjusted it for table use.
If the head is skewing on the columns and jamming, check if there is dust trapped between the column and the far end of the motor housing. This can cause the motor to skew on the column.