Unable to upload documents from PC to smartsheet

With effect from 17 December 2019 I encountered an issue whereby when uploading a document (from my computer) to a sheet or a row in a sheet, Smartsheet initially shows that something was uploaded (shows a blue tick mark in the attachments pane), but then it promptly disappears. Uploading documents from my PC used to be working 100%.

Has anyone else encountered this issue ? Does anyone have a solution ? Could this be due to a a new version released by Smartsheet ?

Any help would be appreciated.