Plot hole: When Ultraworld first shows up on the Liberator's screens, all scans show it isn't there. Avon explains it can't be detected because it is an artificial planet using alien technology which blocks all electromagnetic radiation from escaping. But the crew are looking at it on their screen - the ordinary visible light we use to see things is part of the electromagnetic spectrum too.
Plot hole: If the "Enzyme Activity" adhered to the hull of the Liberator, how did it enter the ship without causing a hull breach and immediate loss of pressure ? Also, how did Servalan not suspect anything when she boarded, missed Orace and ordered Maximum Power surrounded by green mould?