C22 on a clock line at this point does two things -- introduce slight delay (larger the cap, longer the delay) and filters out glitches on clock.
Never looked at this circuit before so my best guess would be the introduction of a delay.
As Frenchmarky - these rarely fail. BUT they can easily break off if manhandled.
Use a ceramic multilayer cap to replace. Most ceramic disc style caps are becoming obsolete and being replaced by better ceramic multilayer caps.