Blob Cache is activated for the web app.
I have tried this on another site collection and it works.
On this particular site collection, I still see the standard renditions and not my custom ones.
First try refresh page with CTRL+F5 if page changes then
and Flush the object cache
In the Object Cache Reset section, do one or more of the following:
To force the current server to flush its object cache, select the Object Cache Flush check box.
To force all servers in the farm to flush their object caches, select the Force all servers in the farm to flush their object caches check box.
When you select one or more of the check boxes, all entries in object caches will be flushed immediately when you click OK. If you do not select any of the check boxes, caches will manage the expiration of items based on when they time out or are changed in the site.
Go to top level site settings on your Portal
Select Site Collection Administration -> Site Collection Object Cache
Check ‘Force all servers in the farm to flush their object caches’ under object cache reset
Select ok to reset the cache
As soon as you do this, you will find the cache is reset, and all the latest changes will now be reflected on your SharePoint site.