Well done!!! you have already found the issue! I am going to post the whole code to show my mistake.
note the missing line :
if (i >= MuxCCNumber) {.....}
....now included in v 2 which is working very well.
I am very impressed 
PS
One thing it may be apparent from my code is my limitations in coding and whilst trying to resolve this issue I was wandering if I should try and minimise the use of global variables and also create functions(i.e. blinking and blinking fast functions) to keep the code simpler. ... but this may be the subject for another post....
THANKS A LOT!!!!!
mux_and_both_modes_v1.ino (11.5 KB)
mux_and_both_modes_v2.ino (11.6 KB)