if there is a temperature shift I am not surprised, ,,, a side note I looked at six commercial wines yesterday and four of them were showing bubbles in the gravity cylinderI've had wines in bulk for as much as 6 months pop solid bungs.
tell me more, I am using a 12V vacuum/pressure pump now, ? you vacuum off the top of the carboy ?. . Keep up with your k-meta additions as you rack, and go buy a bicycle tire inflator and a box of food safe co2 cartridges. $25 all in. Anytime you need to open the carboy, purge the headspace real good before closing it back up.