Why are only some headphones working?

I am using a Vodafone Smart Ultra 6 (current version VDF-995NB02-NZ10d) with Android version 6.0.1. Before two nights ago I was using VDF-995NB01-NZ07b.

I was using my headphones with no issues at all. There is also no lint in the jack. This issue appears to be software only. I connected my phone to my speakers as I normally do, but the sound only played through the phone's speaker. The headphone symbol that appears at the top was not showing too. I tried a few more times, and did a reboot, but still no luck.

I checked my headphones and they were recognised and all features worked. I tried another speaker, yet it was not recognised. I tried various cables in the house to find that only headphones and a standard input to ¼ jack works.

I thought, as I really want to use my speakers, but can only connect to headphones, I'll use a very cheap pair, cut the wired and connect it to the speakers aux. I plugged in the headphones which worked, then I cut each bud off. They were still showing as recognised and music was not pausing or playing through the phone's speaker. I then unplugged the now cut headphones and put them back in. For some reason, they are no longer recognised and music will play though the phone's speaker while connected.

What is happening and how is the phone even recognising this? I tried other third-party apps to no avail.

This only happened after the software update.