Interesting, -105dbm for the rsrp is a little poor, I usually get from -90 to -70, have you the SXT outside and pointed towards the cell tower? or in the general direction?
I'm not sure if the signal would equate to packet loss, does the connection ever just drop?
LTE works quite fine down to RSRP of -110dBm. Can work even down to -125dBm, but it requires fair RSRQ (signal/noise ratio), at least -10dB. Which is hard to get with low RSRP due to uncorrelated RF noise. Absolute minimum is set by thermal noise. Surely throughput drops with reduced RSRP.
What can happen is that LTE connection breaks because of lack of Tx power from customer's device (can happen if Tx power from cell tower is set too high).
Anyways, if RSRP gets lower, then all the LTE L1 machinery kicks in: RRC and RLC retransmissions etc., which means that IP (running on top of LTE data bearer) only observes longer average RTT and increased RTT jitter, but IP packets should not get dropped just like that. Well, IP packets do get dropped, but the throughput gets really low by that time (because of massive retransmissions on RLC timing out). Definitely much lower than 40/20 observed by @tw31ve ... Mind that all the mentioned LTE machinery is transparent to IP data ... and that machinery makes LTE more resilient to interference than any 802.11 stuff.