MK II light strikes

My MK II has just recently started to give me light strikes. I had one last week, one the week before, and 3 tonight. In all 5 cases, the cartridges were put back in the mag, and fired as expected.
I've had the gun for many years, and it has never failed to fire any type of ammo. In fact, I used to take all of the FTF cartridges from others (from their Pardini's, Smith's, etc), and they always went bang on the first try in my MK II.
Here are all the details that I hope will allow someone to provide some answers or suggestions on what might be the problem.
The gun has been cleaned, so I don't think that is a contributing factor.
Ammo is CCI Standard Velocity - from an old brick (7 years old) - it has been stored in a military ammo can, in a steel security cabinet, in a basement that has humidity control to keep it below 60%.
Shooting outside, with humidity 80%+, temp around 70 F. This is really the only thing that is different. Prior to these last three weeks, I always shot indoors with the MK II.
Other than these few FTF's, the gun has performed flawlessly.
Any ideas?
Thanks in advance.
dennis

does the ammo "drop in" to the chamber??? there is clean , and there is CLEAN,,,,,,any divots or burrs on the chamber mouth ?? the firing pin 'tip' is there? not broken......is the top (receiver) on the grip frame "straight" not tilted or canted to either side, (this happens with TIGHT ones, and may cause the hammer to "drag" on its way forward, within the slot of the bolt....there are a few things to look for with any 'rimfire' and after cleaning, comes the ammo , then the magazine, other than any mechanical issue............

Thanks, Dan.
I will check out those things.
Appreciate the feedback.
dennis

Have you disassembled and cleaned the firing pin? I started having trouble with light strikes after a few years without doing a complete clean. Watch that tiny little spring in the firing pin channel. I dropped mine in a pile of wood shavings out in the shop. Got real lucky and found it.

Thanks Single-Sixer...added that o the list of things to do/check.

OK. I spent some time last night field stripping and cleaning my MK II, paying special attention to all of the suggestions above.
!00 rounds this morning, and no light strikes! WooHoo!
I don't know what specific thing was the culprit, as nothing appeared to stand out as the probably cause.
Thanks again, Dan and Single-Sixer!

My money would be on the firing pin and the channel it resides in. I don't disassemble and clean it every time I field strip, but if I am getting any failure to fires, the firing pin comes out. I have had a small percentage of Federal bulk pac rounds that haven't gone bang this year. They have good hard strikes on them, and usually go bang the second time. I went ahead and cleaned the firing pin when I started having some of these. Didn't help, but I am convinced that the problem, in this case, is poor QC with the current flurry to produce .22lr to meet demand. None of the CCI rounds have failed to ignite the first go round.

One of those things you'll NEVER know exactly "why"...as I noted all too often we had simply taken the receiver off ( the upper) looked it all over, everything is FINE ,put it back on and they work...one of my Marine Corps armorer pals years ago, told me of the simple upper on ,canted, slight tilt , and cause the hammer to drag on its ways forward???NOTHING else......
(the hammer rides in the bolt slot, and if "off", can drag...........)