Airdrop not transferring all photos

Hi I am trying to air drop files from an iPhone 7 Plus to an iphone 6. Both are on ios11. THe iphone 7 says sending 42 files and all sent. The iphone 6 only received 19 files - i tried again and only 4 files received but 42 still sent. I have been transferring heaps today via airdrop and found that i could only do 200 at a time - and that was working fine and I literally was on my last 42 to transfer and got this issue! I have checked how much storage my 6 has - its 128gb and has 38gb available so i know thats not the problem. I have restarted each device and that hasnt helped. I sometimes get a message on my iPhone 6 saying airdrop failed and would i like to save to my iCloud Drive. Any ideas on why airdrop isn’t working??