Weird question about messaging app Samsung S9

[Android Central Question]

I tried switching my messaging app from the stock Samsung app to the Google messaging app. After switching all of my previous attachments I sent were re-sent to my contacts. I got no notification of this, only my friends calling me asking why I was re-sending stuff they already got. So I switched back to the stock messaging app and I received duplicate messages from contacts that I had previously received, some with attachments, some just plain messages. Does anyone know why this is happening? I'd like to try a new messaging app for some different features but I don't want this to happen again. I talked to Samsung and they had no clue what I was talking about so they were no help. SMH!!!