Using three external third screen screen recognizes no higher resolution than 640x480 with WD19 base

@lamy-v  The Latitude 5400 only supports DisplayPort HBR2 over USB-C, not HBR3.  If you take a look at the WD19's documentation available on support.dell.com, specifically the Display Resolution Support table, you will find that with an HBR2 system, you can only run dual displays up to 1080p.  This is a limitation of the bandwidth available over regular USB-C when using HBR2 and also having the USB-C set up link to carry USB 3.x as well, which the dock does in order to drive the other functions of the dock.

If your Latitude 5400 was ordered with Thunderbolt 3, which is optional on that model, then you could instead get the WD19TB dock, which supports Thunderbolt 3 rather than regular USB-C.  When paired with a TB3-capable HBR2 system, the WD19TB can tap into 4x more display bandwidth than than the regular WD19 and as such can run dual displays up to 4K 60 Hz each or triple displays up to QHD 60 Hz each.

If you do NOT have Thunderbolt 3, then you only have a few options here:

• Connect one of the displays to the HDMI output built into the system, in which case that display's bandwidth requirements won't have to be included over the USB-C link.
• Connect one of the displays using a USB dongle that uses "indirect display" technology such as DisplayLink, like this one as just one example.  DisplayLink transmits video as USB data and therefore this dongle could be plugged into a USB 3.0 port on the WD19 itself and it would still work.  But DisplayLink requires software installation and comes with some drawbacks that can be significant in some use cases.  I've written about those in detail in the post marked as the answer in this thread.
• Replace the WD19 dock with a dock that incorporates DisplayLink technology, such as the Dell D6000.  The D6000 when connected via USB-C to a system that supports video output over USB-C, which the Latitude 5400, can support up to three displays.  When three displays are attached, the displays connected via the DisplayPort outputs would be driven by DisplayLink, and would therefore subject to the potential issues I mentioned above, while the display connected via HDMI would be driven natively by the GPU from the video output wired to the USB-C port, the same way the WD19 works.