Typically, there are two reasons for why this may be happening:
There were no upright positions - Wesper requires 30 seconds of upright time to calibrate its position calculation algorithm. This can be accomplished by standing or sitting for 30 seconds before or after your session.
There might have been patch positioning issues - for your next session, try to keep the stomach patch as close to the center of your stomach as you can, as this helps Wesper calibrate its position algorithm.
There may be other factors which can confound the position algorithm, such as: a non-traditional sleeping posture, such as semi-reclined, or performing physical activity while wearing the patches.