I solved my problem by temporary making myself vulnerable. I created a new wallet with the same seed on the online system and with that I could get the private key for the change address. Does the system need to be online for the proper change address to be generated? If so, how could I possibly sign a transaction where the change address was an input address? So it's solved but I'm confused 

The change address is sill not visible :-(
to make sure I even recreated a new wallet with the same seed and did the create_new_wallet(True) but the change address was not present on that either.

@TryNinja: Yes, I tried that and that's where I get the "Adress not found" error.

@Abdussamad: I did that and get a number of red addresses and the address is not visible amomg them. In the CLI I also did a listaddresses and piped it through "grep 16Zp4m9ZMLf4sXHxxacusaw3wUpMvRLYZB" and I get nothing. BTW, if I few the details of a transaction with this address, it is colored yellow, not green. Does that mean anything?

Thank you very much for helping.

Hi all,

I have an offline computer running Electrum 3.0 that I use as cold storage. I exported the master public key and use that with a watching only wallet on an online system. I had a few coins which I transferred to a new address because I want to get the private key for claiming my BTG coins. I could sign the transaction just fine (see txid 3e2c7a02aa6f2d6e7a804ccdc27794b8b5bfc724669154da1508147ec778c8d1) but when I try to get the private key for address 16Zp4m9ZMLf4sXHxxacusaw3wUpMvRLYZB I get an "Address not found".

While looking at the issue I noticed that using "electrum listaddresses" gives me 45 addresses on the watching only wallet (which includes 16Zp4m9ZMLf4sXHxxacusaw3wUpMvRLYZB) but the cold storage gives me only 28 (and the address is missing from that list).

Any idea how I can retrieve the private key from the cold storage system?

BTW, both systems have Electrum 3.0 on Ubuntu 16.04 but the online version runs it in a virtualenv while the cold storage systen has it installed system wide.

TIA,
Rob