One presumes this is using the Oneworld Explorer?

You cannot return to Europe from Cape Town, even if just connecting.

There is no Oneworld service between Vancouver and Los Angeles (uses Alaska Airlines, not a Oneworld member.)

FRA-LHR-CDG-LHR seems like a waste of expensive OW coupons for such short (and locally cheap) flights.

To include Africa you would have to route BKK-SIN-HKG-JNB-CPT-LHR or some such.

Keep working on it!