Hi Chris, I've searched the forum but haven't found the answer.
My 2x Dell U2415 monitors are still duplicated while I have:
- enabled DP1.2 (MST) on monitor 1
- disabled DP1.2 (MST) on monitor 2.
My setup is as follows: Macbook Pro 2017 >> HP 3005PR Port Replicator (DP1.2 compatible) >> DP to mDP cable >> monitor 1 >> DP(out) to mDP cable >> monitor 2. I've tried the 8 seconds input trick to enable DP1.2 for both monitors as well.
Re: U2415, daisy chain, MacBook Pro, Port Replicator
For Dell to troubleshoot, you need to test the U2415 on a dedicated Windows operating system PC to see if the issue is present. You can see on the U2415 drivers page and also in the U2415 User's Guide that there is no mention of Apple. You should post the issue on the Apple Forum and see what other Apple users have done as far as Apple PC troubleshooting and possible Apple proprietary cabling to purchase.
You should try to test the U2415 daisy chain directly from a PC TB3/USB Type-C or DP or mDP out port. No Port Replicator. If it works in that scenario, the fault is the transition to or from the Port Replicator.