2014 Ford Expedition misfire and possible compression issue.

Need some suggestions on a compression issue on a 2014 Ford Expedition with the 3 valve 5.4L
This is my fiancé's parent's vehicle and her dad and some other relatives did a timing job on it with all new Motorcraft timing parts and all new Motorcraft rocker arms and roller/followers. They also installed a Mellings High volume oil pump.
After the repair the vehicle has a miss on cylinder 5. They swapped coils and injectors with another cylinder and installed a new Motorcraft spark plug and the misfire stayed in cylinder 5.
I checked injector pulse with a noid light on the cylinder 5 injector and it flashes with the truck running.
I did a power balance test with my scanner and cylinder 5 had no contribution at all.
I did a relative compression test with the scanner and all of the cylinders were 0 or 1-2% except for cylinder 5 which was at 24%.
While turning the engine over in clear flood mode while doing the relative compression, the cadence of the engine was not even further pointing to a compression problem. We also checked spark on cylinder 5 and it's good.
Today they pulled the driver's side valve cover to see if the rocker arms were still attached or if they could see any issues while it was running. They said everything looked normal and intact and all rocker arms were moving up and down the same amount as the engine ran.
They ran a borescope down into cylinder 5 to see if there were any valves that were damaged or if anything looked abnormal, but everything looked good.
We were going to do a manual compression test, but my MAC compression test kit did not have the right connector to install a compression hose into the spark plug hole so I ordered one that will be here on Wednesday because no local parts place had one. We will also do a cylinder leak down test once we get the right connector.
My question is what else should we be looking at? They all swear that they set the timing components were set up correctly and triple checked the marks when setting it up. If they screwed up the timing setup, would it only affect once cylinder? I would think that there would be an entire bank affected.
The truck ran fine with no issues before the repair other than it had some startup rattle that quieted down as the truck ran. The only issue they found on tear down was a bad tensioner. The plastic guides were even still intact. Vehicle has around 170,000 miles on it.
Thanks for any suggestions.

A leak-down test is, exactly, what you should do next. All signs point to a loss of compression on #5. The only question is "where is it going?"
If you have a pulse sensor, it would be worth the time to look at an intake manifold waveform while cranking.
An in-cylinder pressure waveform could be very telling of the valve events. 


 

Thanks for the reply. Hopefully the compression adapter I ordered will arrive tomorrow so we can figure out where the compression is going. The other question is also what caused it since the truck ran fine before the repair. I do have a pulse sensor so I may try using it as well.