Are you reading old posts? They may not be the case anymore, those bugs may have been patched already. Even if such bugs exist, the Roblox Dialogue System is ported completely in Lua so you have the power to fix any standing issues yourself, along with being able to modify how it pans out.
I’m not so sure how the support is going for this plugin given that it is not a default tool that comes along with Roblox Studio and the last update was made in January of 2018, though there isn’t much that actually needs to be updated for it. Most functionality is in your hands.
This week a player in my game told me they couldn’t see the dialogue over one of the NPCs, but could see it for other NPCs. I didn’t do anything differently between the NPC dialogues. I’m thinking of switching to use a different approach now.
EDIT: I was using the old Dialog system (not the Beta).
You should definitely switch over to the Roblox Dialogue System as linked in the OP. It is far more expansive, customisable and amazing for your use case. The legacy dialogue system is completely interfaced in CPP; it’s unsupported, it’s hardly customisable, it’s buggy and it’s awful.
Any bugs that may be experienced in dialogues can also be fixed by you alone, which is one of the charms of the system. Having the API exposed to the developer allows for complete control over dialogues.