1) The routers and smartphones have very different hardware and usually the smartphones have better mobile connection speeds than routers. For instance, RUT950 comes with LTE Cat 4 modem and 2 mobile antennas meanwhile, the iPad might have a modem up to LTE Cat 16 and 4 mobile antennas.
I would recommend you to do the testing with a similar device to RUT950 and then compare the test results, in order to determine the performance difference. It is very important to do the testing at the same location and at the same time of the day with the same SIM card, when the device is connected to the same cellular tower, use the same frequency band, and APN. Also, the router's antenna direction and a present load of the base station to which RUT950 is connected can have a strong impact on download bandwidth.
2) Please send a private message with a troubleshoot file attached for further investigation. Note that the troubleshoot needs to be taken from the RUT950 after an unsuccessful attempt to establish a data connection.
3) I was not able to reproduce the WiFi STA mode related issue on my own RUT950 operating on the latest firmware version (RUT9XX_R_00.06.06.1). During the testing, the router was rebooted 3 times (Main WAN - WiFi, Backup WAN - Mobile) and later rebooted twice (Main WAN - WiFi, No backup WAN). Please send a private message with a troubleshoot file attached for further investigation. The troubleshoot needs to be taken from the RUT950 after an unsuccessful attempt to connect to the WiFi access point.