ResearchProject discoveredLetters are sent again on save load.

[Sn1p3rr3c0n]

If a Mod adds a Discovered Letter then on each game load that letter will be shown again.

<ResearchProjectDef>
...
<discoveredLetterTitle>Sample Title</discoveredLetterTitle>
<discoveredLetterText>Some Text</discoveredLetterText>
 ...
</ResearchProjectDef>

i believe this is caused by the following line: https://github.com/KiameV/rimworld-modifyresearchtime/blob/master/Source/WorldComp.cs#L85
where FinishProject is called for all already completed research.

public void FinishProject(ResearchProjectDef proj, bool doCompletionDialog = false, Pawn researcher = null)
will display a Letter if discoveredLetterTitle is not empty.

this issue was reported to me by: Dalris Othaine. I'm leaving this report so that you are aware of the issue