pppoe connection with multiple CHAP challenges

Hello,
For my first post, I’m encoutering a pretty special configuration.

I’m trying to establish a pppoe connection on a wimax link (could be landline, doesn’t matter)
pppd with rp-pppoe on Linux works fine but the pppoe client on my RB750G can’t authenticate.

So i dumped the ppp dialog on my Linux box and can see multiple CHAP challenges against mutliple concentrators.
For example, there’s PADI/PADO/PADR/PADS/MRU & AUTH config then first auth :
PPP LCP 30 Echo Request
PPP CHAP 60 Challenge (NAME=‘39-034-247’, VALUE=0xb8edf17f206da8af3f9db5c7c558af41)
PPP CHAP 58 Response (NAME=‘139300@numeo.fr’, VALUE=0xdba1157776466dd5e13b0f2aedb60e47)
PPP LCP 60 Echo Reply

Here, the concentrator should give “ok you’re in” (aka success), no ?
But there’s a new config and challenge :

PPP LCP 60 Configuration Request
PPP LCP 37 Configuration Ack
PPP LCP 30 Echo Request
PPP CHAP 60 Challenge (NAME=‘75-002-120’, VALUE=0xd0b6b33869e4409286a908f55dbeb809)
PPP CHAP 58 Response (NAME=‘139300@numeo.fr’, VALUE=0x6af7fe7b54ba41e7f07be181c00ec681)
PPP LCP 60 Echo Reply

Success ??? Noooo, let’s start for a third auth :
PPP LCP 60 Configuration Request
PPP LCP 37 Configuration Ack
PPP LCP 30 Echo Request
PPP CHAP 60 Challenge (NAME=‘PARIS1’, VALUE=0x4cc24abd510c0b5650c61a58e616dee6)
PPP CHAP 58 Response (NAME=‘139300@numeo.fr’, VALUE=0x1e6342a4d8fbae7d8522c59a31472888)
PPP LCP 60 Echo Reply

And finally, we get it :
PPP CHAP 60 Success (MESSAGE=‘Welcome.’)

So, the pppoe client of my RB750G seems to wait for the Success after the first challenge and then end session. How could I debug this ?

Thanks for your help,
Julien