You are using the Monitor Material Coverage Net & Individual Segments and Monitor Material Coverage Net Segments apps, and if you check the same material in both apps, you will see different information.
Standard System Behavior.
It is related to the additional MRP Planning Segments which the apps consider.
Monitor Material Coverage Net Segments:
Considers Planning Segments 20 and 22.
Monitor Material Coverage Net & Individual Segments:
Considers Planning Segments 20, 22 and 24.
Monitor Material Coverage Net & Individual Segments app, additionally considers the “individual planning segments” type 24 (MRP Planning Segment), which explains the difference between apps.
SAP Knowledge Base Article: 2806284 - Different information for the same material in Monitor Material Coverage Net & Individual ...