Problem

Some of the original M+ fonts (1p, 2p, 1c, 2c) have GSUB_Lookup named ligalookup01, which ligatureff, fi, fl, ffi and ffl into \ufb00, \ufb01, \ufb02, \ufb03 and \ufb04 accordingly.
(M+ 1m, 2m and 1mn do not have ligalookup01.)

Since NerdFont 2.0, Material Design Icon replaces these glyphs (\ufb01 is phone_classic!), these ligatures do not work properly.

By removing this subtable manually with fontforge, this problem was solved.

Solution

Add config.json to remove ligalookup01 subtable.