I'm in Melbourne and I've had both i1pro and i1pro2 and all the different kinds of scanning boards, original, updated i1pro and now the i1pro2 board and never experienced the type of issue you're mentioning. Have to say, seems a bit strange. Might have something to do with your scanning technique perhaps?
When scanning, I always scan 'upside down', as in I turn the 1st line of patches is toward the bottom of the scanning board, not the black clip end. I let the paper hang over the edge of the black clip and simply let the sliding ruler hold the paper in place - and the edge of the white scanning board. This way, the spectro or one's arm never touches the next line to be scanned. Eventually, the paper comes far enough down, say about half way through on an A3 or A3+ sheet, so that I can use the black clip and hold the paper in place. I guess this might sound pedantic but it's more from the old days of the original i1pro board, where the head of the device would often touch and scrape on the paper when scanning. The i1pro2 board has completely eliminated this to my knowledge. It seems to hold the spectro at the correct and same height throughout the scanning process. Obviously it's been made this way, specifically to eliminate the problem I mentioned.
Anyway, honestly don't know about the humidity having an effect but if you have a steam gun, that might be useful to clean your board and easier than scrubbing with metho. I've used my steam gun to clean my board once when a friend spilt something sticky on it. Thankfully there wasn't any paper in the board at the time.
Oh, just another thing, I've always done is to keep several blank/unprinted sheets under the one I'm scanning and these stay clipped in.
Hope this helps somehow.
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