Many of my contacts keep being erased for no apparent reason, how can I stop this?

[Windows Central Question]

Many of my contacts keep being erased for no apparent reason

I have had the phone, Microsoft Lumia 640 for 3 weeks and on 4 seperate occasions, over 70% of my contacts have simply vanished from my phone.

 

[PepperdotNet]

Where are your contacts stored? Are you syncing them with a cloud service?

 

[Barstow15]

Are your contacts stored on an SD card? It seems SD card storage is giving some 640 users some grief from what I've been reading here in the forum. It could be bad SD cards or software glitches. My contacts haven't vanished but any new pictures I take on my phone (from 3 weeks back) and any images I save disappear from my camera roll within 24 hours. I have OneDrive set up to save my pictures and saved images so all is not lost.It's just annoying.