I believe WGBH increased their power sometime over the weekend. Check it again - I’m also in the Boston market and couldn’t get 2.1 for a while. As of yesterday (Sunday) I’m able to get it again reliably (25 or 30 miles from their tower).
Also, when I first got my Tablo a few weeks ago, channel 15 (NBC Boston - WYCN at the time) didn’t have guide data for me. I used Tablo’s ticket system to report that issue and within 3 or 4 days it was fixed.
You may want to try that also.
One last thing - for the repack, WGBH moved to actual channel 5 (still virtual channel 2), which is a Low VHF frequency. Those are notoriously difficult to pick up without a good VHF antenna.