Strange Printing Fault Or Flaw?

Could somebody tell me what has happened to the print of the 2nd stamp?
It is a strange one as the cancel looks to be on top of the fault.
It looks like it happened before the cancel was applied.

Could something have been spilt on the stamp before it was attached to the envelope for mailing?

That is possible BlackJag that the morning cup
of tea interfered with the stamp.
It does not look like a spill but it would if
the hot cuppa was wiped off the stamp.

It is a strange one!
I have seen nothing like it natural or played with.

Any indication on the back of the stamp that there is a flaw in the paper? If the absorbency of the paper were affected by an inclusion in the paper making process or if there were surface contamination by oil or even dampness??? it could affect the way the ink was absorbed by the paper when it was printed. Looks so restricted though. Something on the original envelope that leached through the paper and bleached those areas? Or a spill that happened and dried before the envelope was mailed? All speculation.

Thanks backroads a very well thought out reply.
Nothing has gone through the back of the stamp.
Where the ink looks like it is missing the surface
is very smooth compared to the full inked area.

On some damaged examples I have poured some hot water
on the face of the stamp but nothing seems to have happened.

Have favoured thin paper lint type of a fault on the surface
of the paper which has only let some ink onto the surface of the stamp.
It is interesting that you see this as a possible cause as well.

It does look like a strange "Tin Shed" or "as it was printed" type fault.

Gave it another look and came up with this. Chalk would do it and if it was used to mark the paper stock for some reason and then was brushed off to clean the paper before printing, it would still fill the paper fibers and result in lighter inking. That might even explain the look of "lines" drawn on the paper.

And it would completely disappear in soaking and leave no trace.