Here is the google translate from the devs.
About the problem that the client can not start normally under the specific environment in Windows version (7/2)
Currently, in the Windows version, when launching in DirectX 11 mode, depending on the environment of the PC being used, an error is displayed and it has been confirmed that the problem that the client can not start up has occurred.
Previous research has shown that this issue is adversely affected by limiting the drawing limit to 90 fps. We apologize for any inconvenience this may cause you.
Currently, as a temporary response, we are preparing to be able to quickly rewind to the state before patch 5.0 and avoid problems that can not be started due to errors. We are preparing as a top priority with very high urgency, so please wait for a while. We will notify you again as soon as we arrive.
In addition, I would like to explain about this issue, the future response, and the reason for limiting the drawing limit upper limit to 90 fps.
■ About this problem
This time, in Patch 5.0, the upper limit of drawing limit is limited to 90 fps, but the 90 fps limit adversely affects the combination and settings of the monitor and graphic card that support the refresh rate exceeding that. There has been a problem that clients can not start up properly in a departmental environment.
Although it was a change in the basic part of the system, it was not a process that could be widely handled in various combinations including monitors and graphic cards, etc., and verification in various environments was lacking In some cases, I was not able to discover this issue before releasing it. I am truly sorry.
■ The reason for limiting the drawing limit upper limit to 90 fps
When we decided to produce the new version of Final Fantasy XIV, we started producing it on the premise of stable operation at 60 fps as a result of taking into consideration the various environments at that time and the situation after that.
However, in the last few years, monitor performance has grown dramatically, and high spec monitors far exceeding 60 fps have appeared. As a result, when playing at a high fps, problems such as collision omission (a phenomenon in which topography data is not properly processed and slips through the topography) and measurement of actions are not performed normally will rarely occur. Yes.
As a result of investigating and analyzing the client and game processing, it was judged that it would be stable if it was up to 90 fps, and the upper limit value was restricted to 90 fps at the timing of patch 5.0 this time. Even though I have been limited for safety, I am very sorry that I would be inconvenienced on the contrary.
■ About future correspondence
In the future, we would like to consider to be able to respond without limiting the upper limit value, but long-term development is required for the solution, so first of all, as a temporary response, we hurried to patch 5.0 before We are preparing to be able to rewind to the state and avoid problems that can not be started due to an error. We are preparing as a top priority with very high urgency, so please wait for a while.
In addition, although it will be in the state where the upper limit of the drawing limit disappears by rewinding, I do not think that it will develop into a serious fatal problem at the latest. If you encounter problems such as missing collisions or incorrect measurement of actions, it would be very helpful if you could report a defect, including your environmental information.
We deeply apologize for any inconvenience this may have caused.