I have a similar problem only much worse. I was born in UK as were all my ancestors but family search is telling me that I have just a handful of relatives in UK and several hundreds in USA. I am only aware of 3 family members emigrating to Canada 130 years ago and their only descendants all living in Canada. However I am also aware that someone in USA has connected me to families in Yorkshire who have no connection with my family in Birmingham except for having the same names and similar ages. This is mainly because the census records for Birmingham have mostly been incorrectly transcribed with wrong surnames. I knew from family records that they were all born in Birmingham and have birth certificates to prove it as I have the originals and I knew where they lived as I stayed with them 75 years ago so I searched the census record for the correct addresses and found them showing the correct surname but the transcription were appallingly bad and had 3 different surnames in 1860, 1870 and 1880. In another instance my Grandmother's sister took in several homeless orphans when she was in her 60's and 70s, mostly youngsters who did not even know their own proper names so she wrote on the census forms that they were adopted. The enumerator gave them all her surname and the transcribers left off the adoption information. When they came of age they were put on emigration ships to USA and Australia and have been unwittingly accepted as related to me when in fact there are no blood ties at all. As fast as I correct these errors on familysearch I find more people are reconnecting them again
Oh my goodness, that sounds very frustrating! It doesn't give a lot of hope for being able to fix issues with our family trees once and for all if anyone can go on and add/change things at will!