We have been getting a number of reports from end users related to Chrome update 74 blocking uploads from the Bulk Upload Gadget. The uploads work fine from other browsers.
As a result, we have pulled the new Bulk Upload Gadget from the 5.4 release into the 5.3 patch stream and are actively testing it to be delivered in an upcoming 5.3 patch.
In the meantime as a work around, either don’t update to Chrome 74, use Firefox or another browser, or upload assets via the Image or File asset in the finder.
Here is a link to the Preview post of the new Gadget:
Thanks for your patience as we work to resolve the problem.