%<>% isn’t exported by dplyr (only
%>% is). You need to load magrittr instead.
Your reproducible example is running into a subtle magrittr bug, which causes the evaluation of pipeline expressions to search for some operators in magrittr’s scope, rather than in the calling scope. That way,
x %<>% y %>% z, which evaluates as
`%>%`(x %<>% y, z), finds and evaluates magrittr’s