The thread linked below seems to be the authoritative source for Model 3 charging speed limitations from the car. The station, in your case ChargeFox, may limit the charging speed as well.
I know it's been fairly warm lately so this is unlikely but just in case - did you arrive there with a cold vehicle/battery? Rates are controlled by the vehicle to be relatively lower until the battery gets warm.
I've seen my S throttle regen from about 15 ambient which would suggest it would also limit charging, but after that much driving it should have definitely been at optimal charging temperature. On my S I find that if I program the next stop as an actual supercharger it does even more preheating approaching it and the charge always runs flat out for longer (128kW of 130 max till 45% then gently lowers and around 90kW by 63%) whereas if I pass by a supercharger while driving without programming the stop in nav it throttles much sooner. However I wouldn't expect under 50kW by 63% even in that scenario, but we do have different sized battery packs as well.
The ludicrous+ button will start heating your battery. It's not intended for that purpose, but you sure can use it in that way. Just remember to turn it off once charging since you no longer want it running (unless you want it in + mode afterwards.) Of course heating the battery will consume charge so don't do it if you're running really low but otherwise it will be offset by faster charging once you get there.
