I’m on a laptop, not mobile and I don’t see the images either.
Where are you hosting them? It looks like you’re pointing to iconsdb.com even though the instructions there say to not hotlink. You should be downloading and hosting the images somewhere.
As an aside, the reason you see it locally is because you’ve been to the iconsdb.com website to get it and it’s stored in your cache. If you clear cache you probably won’t see it either.
I verified by going to their website with the link you have for twitter. After doing that I was able to see that image on my laptop…still not the other two. Once I cleared cache, I didn’t see the twitter icon again.