23andme had little data on my fathers side so it split my mothers side into my family tree at the great grandfather level. I spent awhile tracing people only to discover my father and mother side seemed to be related. After going on Ancestry I was able to figure the mistake.
Myheritage had European links. 23andme North American links. Ancestry had everything. The genetic time period they match against are different. 23andme matches against 100ad while ancestry 1200ad. So if you are Celtic perhaps your people were in Spain in 100ad but in Ireland or Scotland by 1200. Using different services gives you a fuller picture and understanding of human migration and your migration. The difference from 23andme telling you you are broadly northwestern european vs Cornish/Welsh/Scottish is huge but illustrates what you match against really changes your identity.