ID 468582 - When playing back 4K 60fps sequences in Nuke Studio, the frame rate will fluctuate between 59 and 61fps

Problem summary
When playing back 4K 60fps sequences in Nuke Studio, the frame rate will fluctuate between 59 and 61fps.

This issue occurs even if the RAM cache remains far ahead of the playhead. 

This has been reproduced with EXR sequences (both DWAA and ZIP1) and a DPX sequence. 

Customer reported version
Nuke Studio 12.2v3

Customer reported platform
CentOS 7

Steps to reproduce

1) Open Nuke Studio.

2) Import (File > Import File(s)...) and drag it onto the Timeline.

3) Set the sequence Frame Rate to 60 and the Output Resolution to 4096x2160 (4K_DCP)

4) Play back the sequence and notice that the fps counter will sometimes fluctuate between ~59 to 60 (the fps counter will flash red to indicate this). 

Expected behaviour
Nuke Studio should maintain 60 fps playback for frames that have been cached to RAM.

Actual behaviour
When playing back 4K 60fps sequences in Nuke Studio, the frame rate will fluctuate between 59 and 61fps.

Workaround
Unknown.

Reproduced by support

This bug has been reproduced in:
Nuke Studio 12.2v5 - Windows 10 - Linux CentOS 7

Nuke Studio 12.0v1 - Windows 10 - Linux CentOS 7

Nuke Studio 11.3v6 - Windows 10 - Linux CentOS 7

Earliest version tested
Nuke Studio 11.3v6
- Playback struggled to achieve 60 fps at 4K in this version