We fixed a bug recently where a URI that begins with numbers will not resolve. That's fixed in the latest player versions, but if you're on Windows 8 and higher, Microsoft chose to not deploy those builds. You may need to license a build from Harman to gain access to ActiveX installers for Win8+ with this fix.
The AllowListPattern directive requires at least two levels of specificity in the domain (e.g. *.something.com). I think in this instance, you might be getting stuck on that, and not the bug about domains that start with numbers. Instead of depending on the DNS search path in your network configuration, use the whole hostname when accessing the URL (and in the corresponding AllowListUrlPattern directive).
The first is ok :
SWF : *** AllowListPreview: AllowList allows 'http://123.monsite.fr:8080/tree_grow_small.swf'. ***
And the second is not allowed :
SWF : *** AllowListPreview: AllowList blocks 'http://1234.monsite.fr:8080/tree_grow_small.swf'