Cream sludge in Magnaclean Pro 2 cap

After recent upgrades & changes to a not-very-well maintained open vented system, which included the pro 2 and a new mpv, I did a regular check of the pro 2. What I found was masses of sludge (which I kind of expected, with improved flows, etc.), but what was unexpected were the chambers in the underside of the cap full of a pale cream sludge - not unlike what you would get from weeks-old milk.
This must have affected flow, but otherwise everything else seems ok.
Any clues as to the origin of this deposit? Should I be concerned?
Many thanks.

Most likely system cleaner that has not been flushed out correctly.

Could be limescale affected by the cleaner which has dissolved to a sludge maybe?.Bob

Have you added leak sealant in the past? Could be that.

Thanks for the responses - my guess is that it's cleaner which has not been cleared thoroughy. This was added months ago to try & kick a comatose system into life. Since then I've done some upgrading (increasing a 15mm loop to 2 big rads to 22mm; renewing the mpv; the magnaclean pro2; resiting the OSV & 15mm feed to the flow ahead of the pump - both were located in totally random places &, of course, added fresh inhibitor).
So, we get something approaching a decent flow/temperature, but this deposit was a bit of a surprise. I guess the revitalsed system has finally got to remote corners!
I shall keep watch.
Cheers