Slow Preview AE CC 2021

Hello,

I am coming with two problems related to After Effects.

1. (less important issue) I am using two different PCs for my work and preview is slow on both on them. 

2.  (more important issue) Whilst I have no issue waiting for preview until it's finished, when I preview already rendered preview, I am still coming into trouble with sound, which (they happen randomly, sometimes only one, sometimes both at once):

- crashes for a moment and then just "skips" crashed part to "catch up"

- slows down for a moment and then speeds up for a moment to "catch up"

Visual part is not affected here, it's only the audio, that can't keep up with already rendered preview.

I have tried launching same projects from three different PCs (different specs), different drives, even changed preview resolution to "render every 16 pixels", but the issues are still there. 

Any help appreciated, as I have projects, where catching the sound up with visual part is extremely important, but I am unable to do it, due to issues above.

Thanks in advance.

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Specs:

PC #1:

OS: Windows 10

GPU: RTX 2060 (6GB VRAM GDDR6)
CPU: Xeon E5-2640 v3 2,60GHz

RAM: 64GB RIMM-1866MHz

Drive: ADATA SU800

PC #2 (laptop):

OS: Windows 10

GPU: GTX 1050 (4GB VRAM GDDR5)

CPU: i5-7300HQ

RAM: 24GB DDR4-2400MHz

Drive: Samsung EVO 970 (SSD NVMe)