Adding custom cover doesn't work

I've been on Notebook for a long but each time I try to add a custom cover to a notebook I create, it takes a big amount of ti to process it, and then when it is already uploaded, I select it, however sometimes the cover doesn't even change, and other times, when I restart the app or I check it in another device, It turns out it did never change the cover! I don't know how to solve it, I've tried repeated times but I just cant have custom covers

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Migrate your Notebook data to the new, mobile Notebook.
Zoho Notebook is transforming. The new version will include exciting new features and a completely new user experience. The initial version will be mobile based, available for Android and iOS. A new web version will be available after the initial mobile release. With the release of the new Notebook approaching, we're migrating most of your current data to the new version. Once the new version is released, there will be an additional window to migrate your data. We will not provide access to the