there are so many issues at play here - firstly, discolouration and fogging etc would have nothing to do with your exposure times ... you say you've now ruled out safelight or light leak fogging, and say you've got the paper to work fine now (unless it was just the first few sheets that had become fogged), so I suspect it was a chemical issue - always use fresh for each session and you should avoid any problems along those lines. Also, dont forget to really clean your trays well - you may find the problem was due to contaminated chemicals from dirty trays/ measuring beakers etc. that may also account for the lack of contrast - a contaminated developer can heavily affect print contrast.
As for general contrast issues ... I take it you are using multigrade papers? how are you controlling the contrast? a colour head? a dedicated VC head? below or above the lens filters? if so, which manufacturer? how old are they? Very old contrast filters lose their colour intensity and effectiveness.
A good way to approach printing with VC papers is to use time/ exposure to control your highlights and filters to control your shadows. So do a test strip at g 2 concentrating only on the highlight areas. Choose the time that first shows the slightest of tone in your highlight, then print a whole sheet and look at the shadow areas - too light, then increase the contrast grade, too dark then decrease the contrast grade. Depending on your technique and gear and necessary contrast, you may find you have to work out a new exposure time for each change of contrast grade (I find grades 1-3 need little, or any adjustments in exposure - grades 4 and 5 clearly need an extra stop of exposure but I find they need further fine tuning on top of that, as do grades 00 and 0).
I hoep you resolve it soon - these kind of unexplained darkroom problems can drive you mad.
