Easiest place to start is to shift the bike into it's high gear while it is on the stand and release the cable from the derailleur to check it's tension as the Cyclone does not have a barrel adjuster... you don't have to remove it but just loosen the pinch nut.

Check the position of the derailleur to make sure it is lined up and straight and if this is the case, shift the derailleur manually (by pushing it sideways) when you are turning the cranks to make sure it drops back down into high gear.

If it does this without the cable attached and the problem recurs when you put everything back together then you need to check the cable housings, shifter, and routing under the bottom bracket.

The guide under the bb can get very dirty and prevent the cable from moving smoothly... and if the cable that leaves the Barcon has poorly finished ends the cable could also be hanging up here or there may be a problem in the cable housings themselves.