I'm a rank amateur, so consider that with what I say here. ;)
It sounds to me like it might be that your technique slips after a while. Remember that in a many cases, the ingrowns are caused by the whiskers being cut off short (at or below skin height) and/or ending up with a sharp point that guides back into the skin. Also, assuming that nothing is changing in your prep or lather, it's not very likely that the problem is with the accoutrements and hardware.
I'd go back to the first razor and see if things work well for a while again, before going to a new razor. If they work, then the technique is probably the root cause.
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