When your M2E Pro items are added to the Amazon Repricing Service, ensure that they are updated via a single data source. You should link your M2E Pro Amazon account with the Repricing Tool under Amazon > Configuration > Accounts > edit Account > Repricing Tool. This way, you will avoid double product price synchronization from two sources at once: Amazon Repricer and M2E Pro.
Once the M2E Pro Amazon account is linked with the Repricing Tool, M2E Pro will disable the price update function for the products added to the Service. Such products will be marked with a special icon in the M2E Pro Listing grid:
If you want to update the product price via M2E Pro again, use the Remove Items action in the Seller Central View Mode to delete it from Amazon Repricing Service, or Disable it to pause the dynamic repricing for a while.