I had noticed for a while that the c1ioo frontend model had much higher variability than any of the other other 16k models, and would run longer than 60us multiple times an hour. This struck me as odd, since all it does is control the WFS loops. (You can see this on the Nov17 Summary page. (But somehow, the CDS tab seems broken since then, and I'm not sure why...))
This has happily now been solved! While poking around the model, I noticed that the MC2 transmission QPD data streams being sent over from c1mcs were using RFM blocks. This seemed weird to me, since I wasn't even aware that c1ioo had an RFM card. Since the c1sus and c1ioo frontends are both on the Dolphin network, I changed them to Dolphin blocks and voila! The cylce time now holds steady at 21usec.
Update: I think I figured out the problem with the CDS summary pages. Looking at the .err files in /home/40m/public_html/summary/logs on the 40m LDAS account showed that C1:FEC-33_CPU_METER wasn't found in the frame files. Indeed, this channel was commented out in c1/chans/daq/C0EDCU.ini. I enabled it and restarted daqd. Hopefully the CDS tab will come back soon...