Why are my earphones only sometimes detected by phone?

[Re Boi]

Hello all!

Earphones: Audiofly AF33C In-Ear Headphones
Phone: Huawei Nexus 6P

Info in relation to problem:
- Brand new earphones that have been used on two Android devices and an IOS device without fault. (Using the same application - Spotify)
- Whenever I use it on my phone it rarely detects the earphones and will play music via the speakers of the phone.
- Have used other pairs of earphones which do not have this issue.

- Main difference between the android devices are:
- Different operating system update - my device (Huawei Nexus 6P at Update 8.1.0) and one of the other phones (Kogan phone of unknown model name but running Nougat). Second tested phone (Oppo phone of unknown model name) is running 6.0.1.

- I have checked, and according to the retailer’s website it is both compatible with Android and IOS devices. The manufacturer does not (unless I am blind) detail whether it is or not.
- I have checked multiple settings on what could be impacting it but I couldn’t find anything (unless I am blind).
- Have restarted phone multiple times and switched to different users but no change.
- Appears to be no obstructions in the audio jack.

Appreciate all the help I get!