Were there any 3 way switches involved with what you changed? Did you put any "smart" devices in? When you measure 12V is it 12VAC or 12VDC?
Some smart devices (particularly dimmers) use digital signals, or other internally generated voltages on the traveler wire between the switches. If this traveler is tied back into one of the other AC lines this could cause problems.
GoodBeerFan t1_j215zob wrote
Reply to Need help with a power loss issue by SEND_me_MONEY_4_toes
Were there any 3 way switches involved with what you changed? Did you put any "smart" devices in? When you measure 12V is it 12VAC or 12VDC?
Some smart devices (particularly dimmers) use digital signals, or other internally generated voltages on the traveler wire between the switches. If this traveler is tied back into one of the other AC lines this could cause problems.