Matara to Colombo — train or bus better right now? Any issues with either?

Both are running normally this week. The train is more comfortable for the longer journey and you can actually enjoy the coastal views. Buses are frequent and cheap but can be crowded and less comfortable for 3-4 hours. If you can get a train seat, I'd recommend it for this route. No major issues reported with either recently. The train has been reasonably on time. Buses are always an option if the train times don't work for you. Both are perfectly viable right now — train is just more pleasant for most people on this particular journey.