That sounds like problems I have had in the past.
First suggestion, export mix to WAV file or available file of your choosing.
Put the file on an external storage, like a thumb drive. Load it and play it on a known good computer. ( I take it you are playing this file directly into the board as part of the mix, like you would a backing track or like that. ) If problem persist, might be the board. Return all settings to default or find someone who knows that board. Boards are a specialty in themselves. These are just ideas.

I eliminated a lot of problems, such as latency, when I started using a Tascam or other brand 8-track portable digital recorder. I'll make a Band in the Box track, save it as WAV, and plug the recorder into a USB and drag & drop into a folder on the digital recorder. Actually, you can save each track as individual WAV
and load them one by one onto the recorder's flash card, then load to individual tracks. This would be rare, but for a serious work.

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