Hello!
The block cannot be closed sooner than a list of bets has been updated for this market. This is needed to make sure that conditions such as "Selection's Back Unmatched is equal to 0" have the latest bet data, and to avoid duplicate bets.
In practical terms, this means that the frequency with which a block can be closed must not exceed the refresh rate of the market.
The message you quotes should not prevent the trigger from firing eventually. Look for other reasons.