Bass String Buzz @ 1st & 2nd Fret
Instruments- discuss specific features, luthiers, instrument problems & questions
With a 26" scale, you could 'try' out a .028 wound bass string tuning it to low D. But I definitely wouldn't try thicker than that or it might snap. Your 26 gauge current bass string is already within the high range for thickness. Give it a try- the worst that can happen is it would break the string. Make sure you have spare .026 and/or .024 wound bass strings to put on if the .026 breaks. ;)
Because the .026 is already on the heavy side, you could actually test out a thinner bass string- like a .024 or even a .022 wound. It sounds counter intuitive but remember the buzz started after changing strings. If you have spare strings it doesn't hurt to try this stuff out... strings are cheap.
p.s. did you buff the nut slot with the waxed floss as well?
The bridge is unmovable so I can’t move it. I did however try to see if buzz sound happened when I put on bridge without being in the slot and it still buzzed.
If the buzz still occurred with the string sitting on top of the bridge without being in the slot, that suggests the string action being too low is not the culprit.

but they came out well enough and taste good- satisfying our sweet cravings. We figured out that if we each eat only three cookies per day, they'll last us three whole days. Oh boy!
I did enjoy writing those blog posts.