I believe it is related. I was just having some issues in development where I had installed wp-redis to test out object caching. By installing the object-cache.php to wp-content, you are effectively using a new (better) form of caching for the wp_cache_* functions.
I’m not sure why it’s not an issue with the default cache, but becomes a problem on WPEngine, wp-redis, possibly other memcached plugins… but that seems to be the case.
I asked the wp-redis author about it here: https://wordpress.org/support/topic/unable-to-clear-transients
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