macbook air 1 mail merge problems

I just bought a MacBook Air M1. I installed office 360 ​​because I use mail merge for my clients. I tried to use my database by merging mail but the first client does appear, if I continue merging, they appear blank or Word simply keeps thinking it takes 40 minutes to change the item. Copy the raw database to a new file and do mail merge and it worked, but it slowed down too much. is there any patch? or why is that problem? Aid