That very strange and sad for me that BM818-E1 dont support 1800MZh
I found some leaked docs for BM818-A1 on tests https://fccid.io/2AON8-BM818
There you can see many interesting info about quality of BM818.
In https://fccid.io/2AON8-BM818/Internal-Photos/B18W50495-BM818-Internal-Photos-4107093 you can see that BM818-A1 based on Qualcomm MDM9607 LTE modem (And as I know all IT in Singapore controlled/surveilled by USA).
Recently in Qualcomm chips discovered some vulnerabilities https://blade.tencent.com/en/advisories/qualpwn/
Qualcomm reported that MDM9607 affected by many vulnerabilities https://www.qualcomm.com/company/product-security/bulletins
Does BroadMobi update Qualcomm firmware for chip?