Bluetooth connection app crashes

When I add a timer to the app inventor, it is used to send and receive data through Bluetooth at regular intervals, but the app crashes due to the addition of the timer. Why is this?

If you ask to receive BlueTooth data without first verifying that the BlueTooth Bytes Available in the buffer is greater than 0, you will stall the app until data becomes available.

Doing that in a Clock Timer will have unpredictable effects, like a jammed power tool.