Hello there.
I’m having the same problem that Ann_Sandler mentionned. It started happening yesterday, apparently after Locations was “automatically enabled on all stores” (https://changelog.shopify.com/posts/improve-inventory-tracking-with-locations)
Now, the problem with Ted’s answer is that the option we are looking for is not even in the screenshot that’s in your answer. (The Inventory section had a “Inventory Quantity” field which is what’re missing and looking for.)
Obviously, I can’t make a screenshot myself because it’s no longer within the “bulk editor” for some reason, but you can see the field in the youtube video (2:48 - 2:54) from the This Bulk Editing guide you (Ted) mentionned in your post. (Inventory Quantity 3trd from left)
This option might have been overlooked by the Shopify team/people etc. but it’s the single most important feature of the bulk editor in my daily routine.
Please give it back to us.
Thanks and have a nice day.