Yes it was removed because it contained no value and pdns cleaned them up because updates from your zone would not work otherwhise.
Yes, you have to recreate the record.
If the record is empty - the DNS Master is unable to send the new updated records to the slaves and that renders your zone unusable when you are updating other records because they are not propagated.
What mobile client do you use?
Well, your device is behind a NAT so you are getting a class A network, it is quite common
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