When you list a new product on Amazon via Linnworks, the SKU will be suffixed with .1 if the original SKU is already used on Amazon and is linked with the item in Linnworks. For example, SKU 10001 will be created as 10001.1 on Amazon if SKU 10001 already exists. This is done on purpose, and Linnworks adds a suffix to newly created listing templates to avoid duplicated SKUs. In many cases multiple listings are being created from a single stock item, so in order to keep SKUs unique on Amazon, Linnworks adds an incremental number.
Listing mapping is automatically created and it will not cause any inventory synchronization problems.