Same here. 3rd gen 90kW battery and I typically get 108kW charging rates and slowly tapering down from 40-45% SoC.
Lately I've seen pretty aggressive tapering but I believe that might have been due to the battery temps being already on the high side prior to charging because as soon as I plugged in the fans went on overdrive so I saw charge rates of 108kW for only about 8-10 minutes, then went straight down to 60kW for the remainder of the charging session.
Were you limited before? I have seen weird behavior on my car. Before it was your typical limiting so max was around 94KW. Then a few days ago it went to 8kw when I was at 80%. I initially thought it was tesla wanting me to leave at 80%, so they heavily slow my charge rate once I hit 80%. Then recently it was back to normal again where it would max out at 94kw and charge normally in to 90% when i typically leave.
Still have not seen the 108kw though. We need more data points.
For the record, mine is a S 90D from January/February 2017. I had a few weeks with lesser performance in SuperCharging a while ago (usually around 85-90kW max) but it went back to normal lately, as high as 110 - 112kW sometimes.
In October my 75d would only max out at 65kw. That was after a long distance drive so I know the battery wasn't cold. The fan even kicked in after 5 minutes of charging. When I went to Yellowstone last month, I saw it would hit about 91kw before trickling down.
Not sure if anything changed, but it was nice to not have to sit at every charger for 30 minutes.
In my P85DL we get up to 120kW at some superchargers, but only for about 5-10 minutes and only if the battery is between 10 and 40 or so % SOC, after 30% SOC it does start to taper down... Though I don't know if the taper down has more to do with battery SOC or charger temperatures (the plug does start warming up pretty quick at 120kW) because we generally only use superchargers when on a road trip and so therefore generally only plug into them when our SOC is below 40%
I've seen 100-110kW for longer periods of time (20 or so minutes) but once the battery hits about 65% it seems to taper down to 60-70kW for the rest of the charge...