Great !

Now if you understand why it works (like I said, I don't know much about nginx), let me know.

Argh, this problem should have been fixed in 1.10.1.

I don't know what went wrong, but until I do, you can try launching Ubooquity using the command line and adding the flag described in this comment.

Try these configurations (verbatim, slashes are important):

location /ubooquity/ {
    proxy_pass https://localhost:2202;
    proxy_set_header Host $host;
}

location /ubooquity/ {
    proxy_pass https://localhost:2202/ubooquity/;
    proxy_set_header Host $host;
}

My guess is that both of them will work.

I'd advise the same procedure.

But I don't know a thing about how QNAP Nas work.

Fixed in 1.10.1.

Fixed in 1.10.1.

Version 1.10.0 did not solve the problem in your case ?

My bad, I'll fix that too in 1.10.1 (which will be done as soon as I have an hour to do it).

You're welcome. :)
I'll release shortly a new version (1.10.1) that automatically sets this flag.

I don't know why your version of Java did not include the new color management library used by Java 8 (Little CMS, the missing "javalcms" you had in your log), but if you have this problem, others might have it too.
I'll force Ubooquity to use the old library instead (hence the flag).

Could you try launching Ubooquity with the following command line parameter ?

-Dsun.java2d.cmm=sun.java2d.cmm.kcms.KcmsServiceProvider

Place it after "java", something like:

java -Dsun.java2d.cmm=sun.java2d.cmm.kcms.KcmsServiceProvider -jar ...