@sophiehuiberts@mathstodon.xyz I guess you are numbering your lemmas with the same counter as your theorems? Most packages that do “clever” things with references in TeX use the “reference counter name” \@currentcounter to infer additional information, but if you share counters between environments that won't be enough. There is a section specifically about how to make it work with lemmas (with code) in the zref-clever manual section 10.2, look for the “shared counter” paragraph. The idea is that you locally change the inferred meaning of the theorem counter in lemma environments.