P: Can't import videos

Do you see dynamiclinkmediaserver.exe running in the Task Manager? If not, check if your AntiVirus software are flagging dynamiclinkmediaserver.exe as malicious, try whitelist it if you can.

Does the import always fail on some video files or is it kind of random? Maybe you can try share a few of those video clips online to see if we can reproduce on a different system?

Don't think that's the case, really.
The error I am getting clearly relates to the dynamiclinkmediaserver.exe. Error code (1).
Also, I can import sometimes like 1-5 videos, sometimes none. Sometimes not.


Here is the Mediainfo:

General
Complete name : [...]\GOPR1753.MP4
Format : MPEG-4
Format profile : Base Media / Version 1
Codec ID : mp41 (mp41)
File size : 420 MiB
Duration : 1 min 56 s
Overall bit rate mode : Variable
Overall bit rate : 30.2 Mb/s
Encoded date : UTC 2015-01-01 01:34:26
Tagged date : UTC 2015-01-01 01:34:26
AMBA : x

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4.2
Format settings : CABAC / 1 Ref Frames
Format settings, CABAC : Yes
Format settings, RefFrames : 1 frame
Format settings, GOP : M=1, N=25
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 1 min 56 s
Bit rate mode : Variable
Bit rate : 30.0 Mb/s
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 50.000 FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.289
Stream size : 418 MiB (99%)
Title : GoPro AVC
Language : English
Encoded date : UTC 2015-01-01 01:34:26
Tagged date : UTC 2015-01-01 01:34:26
Color range : Full
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.709
Codec configuration box : avcC

Audio
ID : 2
Format : AAC LC
Format/Info : Advanced Audio Codec Low Complexity
Codec ID : mp4a-40-2
Duration : 1 min 56 s
Bit rate mode : Constant
Bit rate : 128 kb/s
Channel(s) : 2 channels
Channel layout : L R
Sampling rate : 48.0 kHz
Frame rate : 46.875 FPS (1024 SPF)
Compression mode : Lossy
Stream size : 1.78 MiB (0%)
Title : GoPro AAC
Language : English
Encoded date : UTC 2015-01-01 01:34:26
Tagged date : UTC 2015-01-01 01:34:26

Other #1
ID : 3
Type : Time code
Format : QuickTime TC
Duration : 1 min 56 s
Time code of first frame : 01:34:27:24
Time code, striped : Yes
Title : GoPro TCD
Language : English
Encoded date : UTC 2015-01-01 01:34:26
Tagged date : UTC 2015-01-01 01:34:26
Bit rate mode : CBR

Other #2
Type : meta
mdhd_Duration : 116740
Bit rate mode : VBR

Thanks John for the time you are taking to help me, really appreciate it. However, no HEVC codec involved. 
Was this what you were pointing me towards? Or is there more / other parts, too, that I may have missed? 

no. GoPro and Nikon Z.

https://helpx.adobe.com/uk/lightroom-classic/kb/video-support-lightroom.html and especially https://helpx.adobe.com/uk/lightroom-cc/kb/heic-files-support.html#hevc-video-files may help.

Are they HEVC encoded? My guess is that it's because Adobe still hasn't enabled HEVC support in LR on Windows (it was in LR on Mac a year ago).

.mp4 (GoPro - AVC high@L4, 30Mbps)
.mov (Nikon Z6 - AVC high@L5, 50 Mbps)
and others

What file formats?