Hi all, I'm facing similar issue. My issue is replicable perfectly.
1. Remove focus form FFXIV. Click desktop or other applications.
2. Single click on title bar on FFXIV.
3. Issue is occured.
4. If I drag and drop the title bar (move window position), in game mouse cursor works fine.

I'm using Patch 5.21 client but this issue has not resolved.


Hardware Overview:
Model Name: iMac
Model Identifier: iMac17,1
Processor Name: Quad-Core Intel Core i7
Processor Speed: 4 GHz
Number of Processors: 1
Total Number of Cores: 4
L2 Cache (per Core): 256 KB
L3 Cache: 8 MB
Hyper-Threading Technology: Enabled
Memory: 16 GB
Boot ROM Version: 175.0.0.0.0
SMC Version (system): 2.33f12