Repeat bent pushrod on single cylinder

Vehicle was diagnosed with a dead misfire on cylinder 4. Engine would backfire through the intake at times while driving. I won't get into everything that we have done to diagnose our source issue, just the highlights of the diag process. A compression test revealed cylinder 4 read lower than all other cylinders. Removed passenger valve cover to perform a visual inspection and found the purshrod for the intake valve was bent. Technician removed pushrod, manually pushed down on the lifter and felt little to no resistance. Cylinder head was removed, lifter was removed and found to be stuck collapsed. MDS solenoid was removed from under the intake. The pickup screen was found to be clogged with carbon/ usual lack of maintenance. Oil passage from MDS to lifter was inspected and cleaned. The MDS solenoid, intake lifter and all four intake pushrods were replaced. Cylinder head was sent out to a machine shop. No issue was found with the head. Assembled vehicle and test drove. Backfire returned after a short 5 mile drive.

Misfire returned to cylinder 4, compression test found lower compression on cylinder 4 again. We performed a dynamic/running compression test this time. Found slightly lower running compression when compared to other cylinders. Note: We did not do a snap of the throttle when checking running compression. Removed head, we performed a visual inspection of valve train, pushrods, lifters, etc... Couldn't locate an issue. Sent head back to machine shop thinking something was maybe missed. Again they stated nothing was found but offered to do a valve job just to be sure. Received cylinder head back, assembled vehicle and started engine. Misfire was still present on cylinder 4, backfire at times. Technician let vehicle idle while inspecting data on scan tool, performed a couple of throttle snaps and suddenly engine starting running PERFECT. Great idle and throttle response. The vehicle idled in the shop for over an hour like this. Performed final test drive, misfire returned after about 7 miles. 

Misfire returned to cylinder 4. Again performed a compression test, found 4 was lower. Performed a dynamic compression test, running compression was 10 psi lower on cylinder 4. Performed a snap and found reading 105 psi lower. ( No air getting into cylinder four.) Removed valve cover and found pushrod for cylinder 4 bent again.

We have not removed the lifter or cylinder head yet to inspect condition of lifter assembly. Oil level and condition is good. Vehicle has 191233 miles. Any insight would be much appreciated!