After radiator service and repair , there are some occasional bubbles and white froth on radiator. Overflow bottle level also is not increasing when engine is hot.
Sounds like a chemical cleaner was used to flush out the cooling system and they didn't get it all out. Check the hose going to the plastic recovery tank for kinks and being clogged. When the engine is cold, like from sitting overnight, the coolant level in the radiator should be at the very top of the radiator filler neck. Then when the engine warms up and the coolant expands it will force coolant into the recovery tank, which is normal. HTH. -Jim