Pain switching from Brooks to Ergon Saddle

Until September, I’ve only ever ridden MTB on single track, about 3-4 years now. Have put in some really long days on the trail, never get saddle pains.

Then in September I got on TR, just finishing up my first block of SSB1 High Volume, on a road bike/resistance trainer. My road bike has a Brooks saddle, and its quite comfortable. The longest workout I’ve done so far is 2 hours.

Over the weekend in Bentonville I went on a really long haul MTB back-country ride. Ergon foam saddle, Yeti SB6, 40 miles of single track, 3600 ft of climbing, about 5.5 hours total rolling. For the last 1-2 hours, my sits bones were murdering me – the only body part that hurt.

Is the problem the length of the ride? Different saddle? Lack of time on a leather saddle? Are enduro/all trail saddles just bad for long XC style rides like this?

Thanks guys!