No, you will not have to wipe Data with a change of /e/ version - that is only required with an Android upgrade.I will write as if you have TWRP if you have an /e/ Recovery, the steps might be a little bit different!
Transfer the .zip to your SD card (or it can be the phone’s internal storage).
Reboot into Recovery mode,
TWRP will be able to find the .zip by:
Install > up a level > Select: external_sd > scroll to files > Select your copied image …
Note, uncheck, signature verification, I tend to leave unchecked automatic reboot.
Swipe to confirm flash.
Once the flash is reported successful, go back > back,
Advanced wipe of Cache and Dalvic / Art Cache
Then > back, Reboot > System
If this action proves successful it might support the idea that this is a ~v0.19 Regression as proposed by that particular topic - and not the wider issue of a mismatch between Gigaset firmware and underlying stock used by /e/, as suggested by @Didi_6763 in Post #11