@stefaanh , Hi, welcome to the forum!
Please read How to get the best out of this forum, if you haven't done yet.
It is important to provide as much information as possible to get good answers!
Please always provide links to the devices in question, to make clear what you write about.
2.13inch E-Paper HAT (B), 250x122, Red/Black/White, SPI Interface
264x176, 2.7inch E-Ink display HAT for Raspberry Pi
These are the devices I found on the Waveshare website. Please confirm, or post links.
Note that the Waveshare examples use different wiring on UNO than the suggested wiring of GxEPD2.
Connections are made according to instructions.
Please report effective connections used, pin-to-pin.
For the Waveshare examples, tell exactly which examples you used. Link to their example on GitHub is the preferred report.
For GxEPD2 report which example you used and which selection you used.
Report diagnostics from Serial Monitor, in a code window, please (code tags, ).
GxEPD2_Example would provide the optimum information.
-jz-