​The unusual appearance of your FSC-H vs. FSC-A plot is likely due to the low forward scatter (FSC) voltage setting of 50. Such a low setting can compress the signal range, making it challenging to distinguish between singlets and debris or aggregates. This compression can result in poor resolution and a smeared or flattened plot, rather than the expected tight diagonal line representing singlet events. Even though 72% of events fall within gate P1, the low signal strength may hinder proper discrimination. Additional factors that might contribute include poor cell viability, cell clumping, or residual debris, which can further distort the scatter profile, especially under low gain settings. While less common, issues such as detector saturation or compensation errors could also affect FSC signals. To address this, it's recommended to increase the FSC voltage to standard levels, check for clogs or bubbles in the fluidics, filter the cell suspension to reduce debris, and ensure proper instrument calibration and gating strategies for singlet discrimination.​

Refer to these for better understanding😁

https://www.bio-rad-antibodies.com/blog/a-guide-to-gating-in-flow-cytometry.html

https://voices.uchicago.edu/ucflow/2020/09/30/how-to-identify-bad-flow-cytometry-data-part-1/

https://pmc.ncbi.nlm.nih.gov/articles/PMC10802916