In general, issue should be reported to the issue tracker of the respective project (here: osmo-remsim) on https://projects.osmocom.org/ - please make sure to attach all the relevant log files of client + bankd and if possible also a pcap file containing the RSPRO communication.
I cannot comment on the specific scenario, but in general the only known relevant timeout from the 3GPP side is the timeout how long the network waits for the response to an authentication command. This is a very high-level timer and it runs within the MSC/SGSN (2G/3G) or the MME (4G). It includes the transit time within the operator network, the readio network in the UE and the SIM. The default/recommended value is - as far as I remember - 4 seconds. Operators can of couser adjust it differently.
In any case, a detailed analysis should be done, and that should happen in an issue on osmocom.org.
