GAON “the Mishnah Berurah was wrong about how most rishonim held and that were he alive today he would correct the “mistake”? Do you have a source that says this?”
“”See the below link that states so in Anef Bais . Sefer Bais Av – He lived in the times of the MIshna Berurah:””
See also Rav Yisroel Yaakov Fisher (Even Yisroel 8:36). The Bais Av is incomparable regarding the inyan of eruvin (in fact all of his teshuvos are phenomenal).