It seems I've found a bug or glitch in Electrum for Android. I've tried to create watching-only wallets several times. Two of them under Linux and one under Android work perfectly, but another one under Android shows the only transaction to the wallet as "Not verified" despite more than 90 confirmations.
This is a known issue on the PC version. You just restart electrum to make it sync properly. I guess on android you would go to the app view (right most button at the bottom), close and then restart electrum. Alternatively changing the electrum server you are using sometimes does the job.
The cold wallet will not be syncing with servers anyway, because the system will never be online. The only potential problem may be with wallet, seed or signature formats, not with server connections.
There have been bug fixes related to offline signing too since 2.7.9
Also, the issue with networking with servers is generally fairly easy to fix.
The only fix is to install the latest version of electrum on tails. Simply changing servers doesn't do the job.