Did AGNC actually generate any UBIT in recent years? If so, do you know about how much per share for the last complete years? Reporting level (for tax advantaged accounts) is $1,000 in UBIT, I believe.
Think you are confusing MREITs with MLPs. AGNC is an MREIT for which UBIT is not a concept. One must pay a tax on UBIT above $1000 on MLP investments in tax deferred accounts. UBIT is found on line 20(v) of the K-1 for MLPs. MREITs do not issue K-1s. Instead, the corporate 1099 is issued for tax purposes.
All is quiet on your string so far. Some regulars have recommended a REIT in a IRA. It might be to the advantage of more than a few if there was a sell off before ExDay . Be weary of BS stories like the StealingAlpha slop going into a Dividend run. Can a REIT generate UBTZI ? Answer is yes if they don't follow the IRS rules. I have never heard of a problem with AGNC or other major M REIT,s.