This question is not answerable with the given data. After 1.5 days, the chicken should be the same temperature as the fridge (or colder, if not fully thawed).
So we have two possible scenarios, that hinge on the used thermometers
- The fridge is set correctly, the thermostat & temperature probe working fine and the whole setup is not cycling (much) outside the safe zone. That would mean that the thermometer you used on the meat was incorrect and the meat stayed in the safe zone.
- The fridge is cycling outside the the set temperature range. Note that temperature distribution inside refrigerators can differ quite a bit from the nominal value the fridge was set to. This is why some websites recommend that different food groups should go on different shelves, depending on how sensitive they are. In that case your meat thermometer would be correct and the meat unsafe.
Unless you can verify your data with a calibrated thermometer, we have no way to determine whether we are looking at case 1 or 2 here. So from a food safety perspective, we must draw the conclusion that your chicken is not safe. Note that this doesn’t mean that the meat is spoiled, just that the requirements for food safety weren’t met with reasonable certainty.