In FE (→GE,EE) the apparently unclear slur is almost certainly a tie sustaining f2, left erroneously by the engraver – see bar 50. The mistake was corrected in GE2 (→GE3→GE4→GE5).
Compare the passage in the sources »
category imprint: Differences between sources; Corrections & alterations
issues: Errors in FE, Errors in EE, Errors in GE, Authentic corrections of FE
notation: Rhythm