Proto-Finnic *rr
Your inflection module seems to produce past participles like Lua error in Module:parameters at line 360: Parameter 1 should be a valid language or etymology language code; the value "fiu-fin-pro" is not valid. See WT:LOL and WT:LOL/E. for verbs like Lua error in Module:parameters at line 360: Parameter 1 should be a valid language or etymology language code; the value "fiu-fin-pro" is not valid. See WT:LOL and WT:LOL/E., similarly essives like Lua error in Module:parameters at line 360: Parameter 1 should be a valid language or etymology language code; the value "fiu-fin-pro" is not valid. See WT:LOL and WT:LOL/E. for nominals like Lua error in Module:parameters at line 360: Parameter 1 should be a valid language or etymology language code; the value "fiu-fin-pro" is not valid. See WT:LOL and WT:LOL/E.. This is incorrect — *rn > rr was a post-PF analogical generalization (probably mainly based on roots showing the sound changes *ln > *ll and *sn > *ss). Retained forms include e.g. Estonian surnud, older Finnish nuorna, and all cases with *-rn- as a part of the root (such as Lua error in Module:parameters at line 360: Parameter 1 should be a valid language or etymology language code; the value "fiu-fin-pro" is not valid. See WT:LOL and WT:LOL/E. > Fi. kaarna).