MacBook Pro erratic keyboard and trackpad detection MacBook Pro Early 2015 OS 10.10.5 (because of Internet Recovery)

Problem:
So for the last few days the built in trackpad and keyboard of my MacBook Pro have been acting up. After waking up from sleep, they were unresponsive, or didn't respond at all. After waiting some time, they worked again (until next sleep).

Resets:
So in an attempt to fix it, I tried all the resets one get told to do (PRAM, NVRAM SMC), without any effect.

Reinstall:
At some point, I wanted to make a clean install and booted in recovery mode. Here the internal keyboard and trackpad worked 100% of the time. 
That is until I erased the drive. Now only external input devices work at all (even in Recovery).

I even tried Internet Recovery so now I have a freshly installed Yosemite on a erased drive. The keyboard light is working and the trackpad clicks. But Yosemite doesn't detect them at all (Bluetooth Assistant starts since no keyboard/mouse is detected).

Can I somehow check if the driver(?) is installed correctly. Can I totally wipe my Laptop ( Drive, Recovery Partition UEFI)? And would that help? 

Could it be a hardware error, even though it worked 100% at some point in Recovery Mode? At some point I noticed that the keys would work if i pressed them for a long time, but as of now this isn't the case.
To close this up: 

I went to an Apple Store had the logic board replaced. Afterwards, I reinstalled from a backup and everything seemed fine... 

But yesterday I noticed that I forgot to re-enable disk encryption (using File Vault). After enabling it and rebooting I got the exact same problem again. This time I also experienced the problem described here: Password incorrect after enabling FileVault

But unlike last time the problem disappeared (so far) after disabling encryption again. 

If you wind up here looking for answers: Try disabling File Vault and check this for more details: MacBook startup problems - mouse and keyboard not working at login / stuck on apple logo