Due to some technical changes in the product saving hook system, the Fastbay real-time synchronization feature starting from Prestashop 1.7.5
it could be activated several times while saving a product with variations, slowing down the time needed to save it (depending from the number of combinatiosn).

The problem has been reported to the Prestashop team and is being verified, in the meantime, if you were affected by the problem, during back-office operations we suggest deactivating the sync when saving from the module’s SYNC tab and activating the dedicated key via the “Enable Force Sync button in the product sheet” feature on the General tab of the module.

This will allow you to send the eBay sync in the background without impacting the save time and without invoking the module in any way when pressing the “Save” button.

Alternatively, by always keeping the save sync deactivated, you can use the cron “update products since last import” to send via cron the update of eBay products that have their date updated after lasy eBay sync.
(refer to the section dedicated to the product cron for more details on this mode).