The 'exiting on error 17 - image resize failed' exception is thrown in two cases, here:
In light of what you describe, the file does exist and has content so the first case is not the one, but rather, the second. I would suggest increasing the log verbosity in /opt/kaltura/app/configurations/logger.ini to 7 [default is 4], moving aside the old logs, so it is easier to look at new errors, reloading Apache and making the request. Then, look at /opt/kaltura/log/kaltura_api_v3.log and check for debug prints. Specifically ones with the pattern: "Returned value: $returnValue Output"
Also, in relation to the other exception, can you please make sure your memcache daemon is running correctly and perhaps restart it for good measure? And, can you make sure: /opt/kaltura/app/alpha/apps/kaltura/lib/cache/ /opt/kaltura/app/cache/ /opt/kaltura/app/infra/cache/ all have apache.kaltura and 664 permissions on them and that the files inside are writeable to the apache user?