"Frontier says its full-year results for the year ending May 2016 will show revenue of £21.3m, slightly down on the 2015 figure of £22.8m. As a result, operating profit is also down, from £1.6m to £1.2m."
Bear in mind these are unaudited figures tabulated very shortly after the end of their financial year and may not include everything Frontier received in that period, there may also be
UK Government tax relief to take into account.
Case in point. Last year they stated that they expected to post a revenue of £22m with profit of £1.25m in their
Full Year Trading Update in June 2015. This was then revised upwards to the £22.8m / £1.6m figures you stated above once the audited figures were released in September 2015.
You also need to take into account that all the £1.5m they state they've received in Planet Coaster pre-orders will not be included in profits. As it's an as yet unreleased product it will be accounted for as a deferred liability until the game goes gold, only then can it be realised profit. As such any earnings for Planet Coaster (which already offset prior development costs) will end up on the balance sheet for next year. The same is true for things like the Lifetime Expansion Pass for Elite Dangerous, only a certain portion of which is released each year so Frontier can be sitting on money they can't technically touch until later.
The main thing to take away from Frontier's year end trading update is they have a healthy cash balance and no debt.
Planet Coaster was always budgeted for 2 years of development (January 2015 - Q4 2016) so unless the game is behind schedule (which Frontier have stated many times it's not) there's nothing to worry about from a financial standpoint.