Sounds like either your line pressure has dropped significantly somehow, something is blocking the the gas, or you loosened the pilot hood and didn't re-tighten it. Make sure all relevant valves are fully open also.
I don't necessarily agree with DAKSY about the mv numbers you posted. They are a little bit low for sure, but they are far above the thresholds needed for your valve to work and are unlikely to be causing any of the problems you listed. It's still possible that the thermopile is the issue of course, I've seen some with poor / erratic internal connections but to me the original problem at least sounds like a valve issue. I like the "whack" trick because it is repeatable and if it works it almost instantly allows you to troubleshoot something that is otherwise very difficult, and often time consuming and expensive to troubleshoot. If the wack doesn't work, it doesn't mean your valve is fine, but if it does work it 99.99% means your valve is shot. If you do it and you're not sure if it worked or it was coincidence just repeat it five more times to be sure.
As far as your pilot flame's newly developed issue it sounds like some sort of orifice blockage or pilot tube blockage which was causing that irregular pilot flame got worse. That could have been causing poor contact, explaining the low number, and now the issue is causing no contact at all.
I do not know your level of expertise, so I am not recommending you do this. It's up to you to abide by your local regulations and to know your own limitations, as propane especially can be extremely dangerous. With that said, if it were me and I was on a job with the symptoms you have described with the pilot, I would turn the gas off at the valve which is hopefully very near to the appliance. I would then remove the internals / burner etc if necessary in order to disconnect the pilot tube from the pilot hood. I would then test the pilot tube to see if gas is making it through by turning the gas on, pushing the pilot in and observing / feeling / listening / pressure testing the pilot tube. If all seems well up to the end of the tube then you know the blockage is the orifice and a vaccuum, compressed air, a pin, wire brush, tooth brush etc - something can be used to correct the blockage.
If you are unable to rectify the problem I don't think there is any advisable path for you other than purchasing the correct Jotul part through a dealer or online company. Trying to source SIT parts via OEM numbers is quite difficult, and I do not know of any reference guide available to help if the part even exists in the form that you need. There are too many sizes, orientations and other variations to be able to get assistance with this in an online forum, and delayed ignitions or other potential problems if the the replacement is not done correctly or with the correct part can be extremely dangerous.
I did a quick search online, according to this manual (
https://www.manualslib.com/manual/80511/J-Tul-Gf-600-Dv-Firelight.html?page=26#manual) the pilot assembly is 129471. The only listed part is for NG so you would have to either remove the orifice from your old pilot, or order a new one. (129473)
Also, I am not specifically familiar with this make / model; these are my best guesses based off of the afore mentioned manual. Make sure you verify part numbers, and conversion process with the correct manual for the unit.