He probably has just found his line.
mine also started just above the 25th centile, and dropped to below the 0.4th. No issues with feeding, happy and healthy etc.
because she’d dropped more than 2 centiles we were automatically referred to paed. They took bloods, reviewed, found nothing wrong. Conclusion was she’s just small.
feeding advice was to carry on as normal, as much as possible, make sure I had a good diet etc.
I was actually advised by paeds not to give formula top ups or switch to formula because that can almost “force” a weight gain, which can mask a real problem- for example if they have a metabolic disease.
anyway turns out her weight gain went in spurts- if you look at her red book now she gained slowly for 3 or 4 weeks, so her line was nearly flat, then jumped back up the centiles in a week, repeat. By 5 months she was discharged from paeds/gp as totally fine.
if you weren’t weighing him what would your gut tell you? Happy? Hydrated? Wees/poos etc? With dd it was only the scales that was a concern- as my HV said the real concern is if the baby isn’t well along with the failure to gain weight.