Belgian blond ale Duvel

[vertrni]

I brewed two batches of a Duvel clone, a recipe from the cloud site.
One had 1077 as OG, the other 1079.
I used Safale 256 on the first brew, and warmed it up to 23 degrees.
I used Mangrove Jack M31 on the second batch and warmed to 23 degrees too.
The first batch started and is happily bubbling away.
The second is not producing any gas/bubbles. I opened the jar and saw a lot of krausen.
That was approx 26 hours ago. The krausen has diminished a lot, but the wort still does not produce any gas.
I checked the cover and airlock, even replaced them. Still no bubbling.

How is it possible that there is krausen and no gas is produced ?
Both worts are fermenting in a conical Fastferment jar.

 

[Kevin58]

Most likely you have a leak in the seal of your fermentation vessel. The resulting gasses will get out. They don't always go out through the air lock.

 

[McMullan]

Ideally, use gravity measurements to monitor fermentation. It's not unusual for krausen (yeast floccs containing trapped CO2) to hang around for a while after reaching FG. But, as already noted, at this stage, more likely a leaky FV.