Problems with the balance holes of the impeller in Dalian Empire’s single-stage, counter-circulation type shielded pumps

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The year before last, the unit was equipped with a Dalian Empire single-stage, vertical, counter-circulation type shielded pump (RW22-716J4BM-0810W1-H, with a flow rate of 100 m3/h and a head of 140 m). Since the operating flow rate often exceeded 120% of the rated value, the front bearing (located near the impeller side) became severely worn within less than a month, while the rear bearing remained intact. Later, the manufacturer helped with the analysis; they simply enlarged the balance holes on the impeller (there are 5 in total) from 4mm to 4.5mm, and as a result, the lifespan of the rear bearing increased to half a year. I would like to ask the experts: 1. The front bearing is severely worn – could this be due to a flow rate that exceeds the design value, resulting in an axial force acting in the downward direction? What is the simple formula for calculating axial force? What is the impact of excessive or insufficient flow on the front bearing or the rear bearing? 2. The impeller balance holes (a total of 5) have been enlarged from 4mm to 4.5mm – is there any simple theoretical basis or calculation for this? Please provide some references. I urgently need the theoretical and experimental analyses from all experts. Thank you.