I have Stans Alpine rims that normally work really well but I had a Conti Race King that kept losing pressure and thought maybe the solution had gone. So I pumped it up one more time and when I spun the wheel there was a funny sound so I split the bead and there was only 1/4 of a red cap measure left and this amazing lump is this normal? I have refilled the tyre (1 red cap full) and it now seems fine.

What lump? I can't see…..

Hang on I will sort this photo posting in a minute.

Yep, latex will dry out eventually, just bin it and replace

I've had this with JRA wheel milk a couple of times. The second was when fitting the tyre and I'd used CO2 to inflate the tyre the stuff turned into a ball. Not sure why it happens but not related to lenght of time it's been used.

Just swapped some tyres around and I pulled a lump like that out too..

same here, tyres have been on one set of wheels for a year and they are fine another pair been on a differant set of wheels for 6 weeks and gone like that..