+(ч)чен<post>

[hectoralos]

The first ч should only appear in contexts where чен should be read as voiced. So, it has to be deleted after voiceless consonants. Exemples:

$ echo "мулкач<n>+ччен<post>" | hfst-lookup .deps/chv.LR.lexc.hfst 2>/dev/null
мулкач<n>+ччен<post>    мулкач>{ч}чен   0,000000

Generates мулкачччен instead of мулкаччен.

$ echo "автан<n>+ччен<post>" | hfst-lookup .deps/chv.LR.lexc.hfst 2>/dev/null
автан<n>+ччен<post> автан>{ч}чен    0,000000

Generates автанччен: correct.

$ echo "йытӑ<n>+ччен<post>" | hfst-lookup .deps/chv.LR.lexc.hfst 2>/dev/null
йытӑ<n>+ччен<post>  йыт{ː}ӑ>{ч}чен  0,000000

Generates йытӑччен: Correct.

[ftyers]

$ echo "мулкач<n>+ччен<post>" | hfst-lookup .deps/chv.LR.hfst 
мулкач<n>+ччен<post>    мулкаччен   0,000000

In 0f14150