Hello,
I was not able to reproduce the issue regarding DHCP static leases using the latest firmware version (RUTX_R_00.02.01.1). During the testing, RUTX11 was configured to assign five static leases. Three IP addresses were from the DHCP pool range and two of them outside of it.
Could you provide detailed instructions on how to reproduce the issue? Every detail is important.
In the meantime, I would suggest resetting or even better updating your RUTX11 firmware via bootloader menu and check whether the issue persists. Instructions on how to perform an update can be found in Teltonika Wiki:
https://wiki.teltonika.lt/view/RUT9xx_Firmware_via_The_Bootloader_Menu
Note, that these instructions are made for RUT9** series devices, however, the same principle applies to RUTX11 as well.