Since the hard start disappeared right after the new chain was installed, but has since come back. I'd make sure that all the electrical connectors are clean. Take some electrical contact cleaner to all visible electrical connections. There also is a paste you can apply to help prevent any future corrosion on connectors.
My guess is that while replacing the chain, they removed some connectors, dislodged some corrosion, which has since accumulated again possibly due to weather, or moisture around the engine.