High PWM level via UNO (B) on BLDC motor effects UNO(A) irregular move NEMO17

PWM connected to Arduino UNO (B) to control motorspeed of BLDC motor. Voltage 0-5VDC. A separate but connected Arduino UNO (A) is programmed to power a stepmotor NEMO17 via a driver. At a >50% PWM the rotation of the stepper becomes irregular. What is the cause of the unwished induction or voltage leaking?
Any idea how to avoid the induction or voltage leaking? Many thanks in advance.

Problem solved: Both USB sticks connected on one source; PWM can go to 100%

** Both USB sticks connected on one source**

There's no mention of USB sticks in your post.
What are you saying ?

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Reported by NassauLv on Today at 22:38:37. They left the following message:

The combined circuit has two Arduino UNO microcontrollers. Their power (on USB connectors) is, in stead earlier, now arranged from one source (adaptor with 2 ports). That solved the problem. Thanks for your interest to read my question.

A reply in the topic would have been better don't you think ?

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