When /l/ and /n/ come together in a word, generally the /l/ will turn into /n/: so /ln/ becomes double /nn/. Since /l/ is common ending, you will see this pattern whenever it is added to words ending in /n/.
su’nn ‘cranberries’ (comes from su’n-l) su’n ‘cranberry’
signn ‘socks’ (comes from sign-l) sign ‘sock’
It also happens in the opposite direction: when you add /n/ to something ending in /l/.
etlatal I am eating
etlatann you are eating (from etlatal-n)
mesgil I am big
mesginn you are big (from mesgil-n)
This pattern is distinctive to Listuguj Mi’gmaq: speakers from the east do not make this sound change. This is the reason, for example, why Listuguj speakers say /nnu/ while others say /lnu/.
(There is at least one important exception to this rule—seen in words like /nemulneg/ ‘we see you’—more on that when it comes up.)