Intel Mac Mini (2018) and Dell UP2720Q over Thunderbolt - At 1920x1080, what should the refresh rate be?

[Droid13]

Sometimes I get 30Hz. Sometimes I get 60Hz. It seems random to me (the refresh rate can even change during the same work session) and I do not understand how or why this is happening.

System Information (when running at 30Hz):
Chipset Model: Intel UHD Graphics 630
Type: GPU
Bus: Built-In
VRAM (Dynamic, Max): 1536 MB
Vendor: Intel
Device ID: 0x3e9b
Revision ID: 0x0000
Metal Support: Metal 3
Displays:
DELL UP2720Q:
Resolution: 3840x2160 (2160p/4K UHD 1 - Ultra High Definition)
UI Looks like: 1920 x 1080 @ 30.00Hz
Framebuffer Depth: 30-Bit Colour (ARGB2101010)
Display Serial Number: []
Main Display: Yes
Mirror: Off
Online: Yes
Rotation: Supported
Connection Type: Thunderbolt/DisplayPort

System Information (when running at 60Hz):
Chipset Model: Intel UHD Graphics 630
Type: GPU
Bus: Built-In
VRAM (Dynamic, Max): 1536 MB
Vendor: Intel
Device ID: 0x3e9b
Revision ID: 0x0000
Metal Support: Metal 3
Displays:
DELL UP2720Q:
Resolution: 3840x2160 (2160p/4K UHD 1 - Ultra High Definition)
UI Looks like: 1920 x 1080 @ 60.00Hz
Framebuffer Depth: 30-Bit Colour (ARGB2101010)
Display Serial Number: []
Main Display: Yes
Mirror: Off
Online: Yes
Rotation: Supported
Connection Type: Thunderbolt/DisplayPort

Advice appreciated please.

Thanks in advance.

Edit 1: Dell being a somewhat crap company when it comes to Apple may be a factor here.
Edit 2: Have posted System Information when things are running at 30Hz and 60Hz; no changes were made to the physical setup, this is just something that seems to happen.

 

[Fishrrman]

What is your connection scheme?
(HDMI, USBc, etc.)
Have you tried changing that to another?

Could it be the cable you're using?

Have you tried the "Better Display" app (free mode works fine)?

 

[Droid13]

What is your connection scheme?
(HDMI, USBc, etc.)
Have you tried changing that to another?

Could it be the cable you're using?

Have you tried the "Better Display" app (free mode works fine)?

I am currently using the Dell-supplied Thunderbolt cable to connect the Mac mini to the designated Thunderbolt/DisplayPort port on the UP2720Q; sometimes I will get 30Hz and sometimes I get 60hz.

I have previously tired using HDMI; this did the same thing.

I have not tried Better Display; will give it a whirl; thanks.