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In a nutshell: The MIB is wrong, so either request a correct one from the manufacturer or , build one yourself, or patch the existing one. Annoying, but unfortunately, this happens more often...
There are apparently several things wrong in the MIB or with the device (depending on how you look at it), ; in any case, they do not fit together. From the RFC 1213 (https://www.ietf.org/rfc/rfc1213.txt) RFC-1213-MIB.txt:
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There you can see several things: A "DisplayString" can only contain ASCII and can be max. 255 characters long. But the above example is 439 characters long and also contains includes a UTF-8 encoded "รถ" (2 bytes > 127). So the decoder has several reasons to reject the trap as invalid, but nicely it lets it pass, just in hex. Which encoding should it take? There is nothing defined in "DisplayString", ; it could just as well be Latin-1 or a funny Windows code page.
If the device can send really long UTF-8 strings at this point, then there must be no "DisplayString" in the MIB, but something with a TEXTUAL-CONVENTION containing a DISPLAY-HINT of, e.g., "65535t".
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