There is one known HUD issue in v4.9 which completely hides the Tower Build HUD, when you untick ‘TimedWaveStarts?’ from the Wave Handler. This can be fixed by making the missing connection in the Tower Build HUD as shown:
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This fix will be included in the next update, which will be submitted within a week. But from what you’ve said, the bug you encountered might be different from this. Could you please try this out and let me know if it makes any difference?