As a part of v2.3.0 update, extension's structure undergone serious changes.
As a result, if an update from older version to v2.3.0 or above will be performed 'as is' without using Composer, some loose files will persist in extension's folder.
The extension may misbehave or cease to work because of these redundant files.
To resolve it:
- without using Composer: please remove the content of [Magento's root folder]/app/code/Amasty/Feed prior to uploading the package with updated version.
- with Composer: no additional actions required.
Composer will clean [Magento's root folder]/vendor/amasty/feed automatically before installing the update, effectively, removing the difficulity's cause automatically.
Reference for Composer usage is available here.