Your question is State specific, and you would need to consult the probate laws of the State in which the will was filed. The following may not apply in all states.

The gift to M and then over to J might be termed a springing executory interest in some states. This would consist of the gift to M, but she would be stripped of title if the testator had placed a condition on the conveyance the occurrence of which would vest title in J. However, that may be open to question if the will were poorly drafted, and failed to clearly state the wishes of the testator. Normally the testator would set up either a testamentary trust or an inter vivos trust with M acting as trustee for J until he reached age of 25.

I ran into a similar situation during a title search several years ago in Connecticut. There was some question about the validity of the deed. I consulted the local probate judge who indicated that in his opinion the title to the property was conveyed by the will rather than the deed. If the deed were insufficient it was a matter of recording a corrective deed. However, that may be difficult if many years had passed, and may require signatures of heirs to the property if the original grantor had died. His opinion was based on his interpretation of Connecticut law. 

I did a title search on a condominium several years ago. A mistake had been made in the legal description 10 or 15 years earlier. Since that time the property had been sold several times with the wrong unit number listed in the legal description. It was necessary to go back to the grantor of the first erroneous deed, and have her execute and record a corrective deed to the current buyer. Fortunately she was still alive and residing in Connecticut.

I think some inquiry should be made as to the significance of the affidavit of possession. Did M possibly acquire a title interest through adverse possession?

I recall in law school one of my real estate professors talking about Chicago's oldest known easement. It dated back to the time Chicago was a frontier town. One of the local farmers used to walk his cattle down to water them in the river that now runs through down town Chicago. He developed an easement on the property which apparently exists to the present. No one ever bothered to get a deed or release of the easement. It was my professor's opinion that it would require the signatures of all the living heirs of the farmer.

If there was some perceived invalidity with the will, the probate court probably would not have accepted it, and the estate would have been probated as an intestate succession. It would probably also have been subject to challenge by putative heirs. In which case the court would have ruled on the issue.

Since M was the residuary legatee, if the gift to J failed for some reason in Connecticut  the property would fall into the residue of the estate , and pass to M under the residuary clause of the will.

The best you can do in this situation is to report your findings in your abstract, and leave the determination of title to your client and the title insurer