Hi mmosende, and welcome to the MxCommunity forums!
You may try performing a reboot on the T26’s that you are not able to connect to. I would recommend to try searching for the cameras as below;
You can connect to any MOBOTIX camera by using their factory serial number 10.x.x.x/255.0.0.0 or using the search function in MxManagementCenter.
If, by chance you have initiated the Autoconfiguration process, please keep in mind that this usually would cause the T26 to obtain a 192.168.0.19 IP Address and host a DHCP server - It is possible that your other T26 units may now be sitting on a dynamic IP address. You may need to disconnect all other T26’s from your network and connect them one by one and confirm their network settings. It also helps to do this on an isolated network that does not have anything else within the LAN except your PC and T26.
I hope this helps!