No LINK to device using certain NIC's

We have a number of proprietary network devices deployed to different sites which utilise an ASIX AX88796 LF 100BASE-TX NIC.

About half of the devices each connect directly to an HP Laptop's integrated Realtek PCIe NIC using a Cat6 Ethernet patch cable.

The other half each connect directly to a Dell Micro PC via a D-Link Dub 1312 USB 3.0 NIC using a Cat6 Ethernet patch cable.

On a number of the D-Link connected devices we have begun to notice an issue which appears to be progressively getting worse whereby the when the device is turned on first thing in the morning it can take up to 30min for it to be detected (as a LINK / connection) by the PC network adaptor.

During this time the device LINK is more likely to be detected by certain NICs I've tested than others.

Adaptors more likely to detect a LINK:

HP integrated Realtek PCIe Ethernet

Dell integrated Intel I217-LM Ethernet

Adaptors less likely to detect a LINK:

D-link Dub 1312 USB 3.0 Ethernet Adaptor

TPT-8020A Cable Tester

This appears it could be a fault with the device which I hypothesise could be due to failing caps on the board; possibly causing an initial voltage drop which is tolerated by some NICs (integrated) better than others (USB).

I would like to obtain some quantifiable data as to why some NIC will connect with the device when it's in this state and others wont until after some warm-up time and am looking for a way to measure the TX/RX voltages etc of the device NIC and all PC NICs for comparison.

Any ideas what tests could be carried out to determine the connection quality of the NIC (rather than a LINK / NO LINK result by my current tester) or other issues to consider?

(I don't currently have access to a scope but may be able to get hold of one if necessary.)