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you may have tried this already but, I though I would suggest it.
If you are in moderate to marginal wifi coverage it may be interference from another router in the neighborhood.
This may be causing your drop outs. You can test this out by changing frequencies/channels on the router or find an app. that will measure the wifi frequencies around you (unfortunately I don't know of a good one for Apple but, I use Windows 10 free versions of "Wifi Analyzer" and "Acrylic Suite". From the measurements you can hopefully manually select the least used frequency which will have less interference.