[Darryl Ramm]

The front panel jacks are simple low-cost 1/4”panel mount jacks on fly leads. Not hard to replace by somebody handy with a soldering iron and common parts available from electronics component suppliers. They may even just have damaged contacts that might be able to be bent or cleaned. You would normally identify faulty units by just wiggling the plugs, or occasionally maybe a multimeter to measure continuity. With some soldering you may be able to swap around the front panel jacks to temporarily a broken one with one of the unused front panel jacks. (The rear panel jacks are all board mount IIRC so not swappable like that).

I assume you mean reverb added inside the Eleven Rack rig... if the main signal drops instantly and you hear a reverb lingering for a short while then the problem is on the input not output side. There is no way a problem like this could be a faulty output jack (it might be say a faulty output analog stage, or its digital controller, where the whole output level decreases a large amount and you think you are hearing only reverb).

You need to just do careful logical troubleshooting, before even thinking about opening up the Eleven Rack, excluding things like your guitar cable, guitar itself (unintentionally moving it/it’s output jack while you are messing around). Try playing back using different headphones or monitors. You hopefully have a DAW connected to the Eleven Rack and can test with that, disconnect the guitar and just playing a signal generator to the main outputs... physical output hardware and electronics problems will show up with that test just fine.

It’s also possible you have a more serious than just the input jack intermittent problem, if so without electronic repair skills you are unlikely to make progress there. It’s likely not worth bothering then, and not worth paying for local technicians to repair it. If so toss it out and buy a used one online for ~$150.