Maybe this is what is happening:  The California band can only be pulled hand tight.  But the Calcitrate bander, being mechanical, perhaps can put the band on a lot tighter.  Perhaps so tight that it prematurely starts cutting into the skin allowing for a larger and longer duration open wound.  And while it is a localized infection site, it may be uncomfortable enough for them that they slow down a bit like you described.

That is what I came up with after some thought.  Maybe entirely wrong.  I know I would be uncomfortable with those larger open sores.  The good thing is you have them protected from Tetanus and haven't lost any!

Think about trying the band a little less tight.  And/or medicate the drinking water with some Albon (sulfadimethoxine) during (or just before) the time they usually "slow down" to counteract any infection in that larger wound....