In some cases with freezes/delays as you are experiencing, the system may be involved doing something else. It might be video or network type actions or just your system updating itself somehow.
First, I would suggest disconnecting the WD HDD for testing.
Could you give us the make and model of the RAM?
Secondly, watch the network activity to see if anything is going on during the delays.
Any scans happening, such as an anti-virus or updating such as online storage backups?
Since the motherboard is UEFI capable, did you install in that configuration? If you aren't sure, attach a snipping tool picture of your Disk Management window.
Are you using a 4K monitor with it? Are you using some type of combined video using both the Nvidia and Intel video?