Okay... I did my homework and some deductive thinking, and finally found out that a difference between my MySQL local version and the one set up on my host was the cause of all this. It seems that those versions didn’t create SQL comments the same way...
The host setting is using # for comments,
The local setting is using -- for comments
When I imported the DB back via phpMyAdmin, I didn’t get syntax errors, the DB was created "normally" but I had those errors in MODx and all hell went loose...
I re-imported my backup fixing all the comments with the right prefix and bam : it works...
I honestly wonder what the h*ll is wrong with this host, they always have some funny config tweak that causes all sorts of problem... grrrr, lost quite some time on this. MODx was NOT involved...
Thanks Jason for pointing me in the right direction

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