Complex sentence: They also delivered a concept mock-up and was originally thought to be the favourite to win the contract, though analysts were concerned that a measuring error involving the London Underground 1983 Stock during the evaluation period could sink their bid.
Split into simpler sentences: They also delivered a concept mock-up and was originally thought to be the favourite to win the contract. However, analysts were then concerned that a measuring error involving the London Underground 1983 Stock during the evaluation period could sink their bid.