OK,..... Now i can finally summarize the case after the answer from the support ...
It took a long time for support to find the problem .... the first answer was that MA-SFP-1GB-TX it was not compatible with Internet ports on MX250, or something about cables, and finally after a few weeks of repeating from me that it must be a bug, etc .... support agreed
The solution from support: "...we have a known issue with the MA-SFP-1GB-TX module with the Serials 211xxxx not being detected on the WAN interface of the MX250 and MX450 however this issue has been resolve on the new firmware. So in order to get the MA-SFP-1GB-TX module to work on the MX250 the device will need to be updated...."
We tested it (before support gives an answer) and I can confirm that MA-SFP-1GB-TX works with MX250 on Internet ports after updated to FW: MX 16.11 /Beta per now, (it may take a while for the module to start for the first time, you just have to wait).
PS. I also tested 3rd party device 10GB that works OK but instead of 1GB you get 10GB uplink via cobber (works fine before update with FW 15.4.01 and after w/ 16.11):
10Gtek® 10GBase SFP+ transceiver module 30m https://www.amazon.de/-/en/gp/aw/d/B01M8O3MAL/ref=ya_aw_od_pi?ie=UTF8&psc=1
Br
Remi