I have made swiss meringue a hundred times. It is really hot in the NW right now so last night my house was too hot and it wouldn't work. Threw that batch out and got up this morning before the house was hot (75 degrees) and it is still turning chunky after I add the butter! Is there anything I can do to save it?
What are the chunky lumps? Butter?
If its chunky lumps of butter, it should come together with more beating (to warm it up a bit) but if the chunks are egg whites, I don't think you can save it. Most butter related issues will resolve itself with extended mixing on low speed or temperature change (heat if the butter was too cold and bags of frozen veggies/fruit put around the bowl if the meringue and/or butter are too hot). HTH.
I don't understand the chunky part either. I say, keep mixing until the sound of the beaters is about to drive you mad. It will eventually smooth out.
When you say lumpy, do you mean it has a curdled look?
I know you make SMBC frequently, but take a look at FromScratchSF's blog post about it. You may get an idea of what the issue is as well as how to resolve it. Her photos are very helpful. And her recipe is excellent. It's my go to recipe for SMBC.