but not sure of the force of "mir" in the sentence

Well he just wants to say that he himself is not able to give an explanation. Someone who is more "internet-savvy" perhaps could ...

For reasons that are not clear to me, I did not get/receive this message.
For reasons I do not understand, ...

(didn't needs an apostrophe)

I'm not sure if "reason" is the right term. "cause" seems more appropriate to me.

SD3: "For reasons that are not clear to me / I do not understand" suggests that you are too stupid to understand them and not that you can't explain a phenomenon.

@ #4:
I'm not sure if "reason" is the right term. "cause" seems more appropriate to me.

1) Reason(s) would be the normal English translation. "Cause" would be quite unusual, and in my - native English speaker's - opinion, inappropriate unless this were a discussion about technical (e.g., hardware, software) problems. Since the original poster identified his/her question as "Wirtsch." I see no reason to assume that it is.

2) see #2. Was that perhaps not clear to you?

3) "For reasons that are not clear to me / I do not understand" suggests that you are too stupid to understand them and not that you can't explain a phenomenon.
This is, if I may say so, absolute rubbish.

Getting back to the original question, the standard English formula is "for some inexplicable reason." If you, as the speaker, want to make it clear that you are allowing for the possibility that this "inexplicability" may be confined to you, then you need to say something else.

for some reason unknown to me....

also possible - nicely vague ?

Ich kann keinen Unterschied zwischen #1 und #2 erkennen.

aus unerklärlichen/unerfindlichen/mir unerklärliche Gründen heißt alles dasselbe. Selbst wenn er es noch so apodiktisch formuliert, ist klar, dass solche Banalitäten nie absolut unerklärlich sind, sondern immer nur aus der Sprecher-Sicht.

I agree with you, Omar.

The options are

a) I don't find an explication
b) I can find an explication, but it's not clear to me, I don't understand why it happened (SD3 version)

Lars:
The word is explanation!