I see these meter-errors from time to time.
In Dorico a meter can come at any point, even before a bar is complete. Incomplete bars are needed as pickup bars and in various other situations.
In this case, your 3/4 is interrupted by the 2/4. Turn on insert mode, double-click the 3/4, and press Return. (And then turn insert mode back off.) This will fill out the correct number of beats for 3/4. You’ll have to reconnect the tied notes manually, because you added time in the middle of them.
Also you can delete the redundant 2/4 in bar 280.
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Thanks! That wasn’t very intuitive 
I’ll stick to adding a bar the I guess. That solves the missing content.