401k Roth rollover to Roth IRA is being considered a taxable event

This is not taxable, John Hancock is wrong. The 1099-R should be coded as "H". This is very clear in the IRS instructions:

Can you talk to John Hancock directly? Not through your employer, they didn't issue the 1099-R. Get a corrected 1099-R so when you file the "Taxable Amount" box shows 0.

When you talk to them, insist that this be classified as a "direct rollover" not a "withdrawal". These are very specific terms in the IRS rules. One is not taxable, and one is.

If you can't get an updated 1099R go ahead and file your tax return with the correct info: $X rolled over from 401k, $X rolled into the Roth IRA, taxable amount: $0. Absolute worst case is an IRS audit (unlikely), where you show statements and rollover documents proving all of this money is where you say it is. Then tell them JH refused to give you a corrected 1099R.

This question also has more info.