Every social network can breed problems because this is how humans are - a mega colossal mixed bag. What matters is how you perform moderation to ensure minimal conflicts, and/or what kind of community do the heads desire.
Lemmy has become infected with the Reddit illnesses already (neglect of nuanced moderation besides political addressing, Reddit style hivemind voting, posters willingly discarding morality) but certain things like trolling and harassment are somewhat decently dealt with. The problem is that Lemmy still lacks a large userbase, and yet these problems are flourishing.