Your stability issue is probably nothing to do with the modem - unless it is faulty. There can be plenty of reasons however modem firmware/design/chipset is unlikely to be one of them.
... And people have said the HG612 IS better because of the BROADCOM chipset being superior (Or something like that) ...
More fool you for believing them. In some cases Huawei will perform better, on others the ECI - dependent on many factors and I am sure that no one has tested those to against every possible combination.
I use an ECI where the DSLAM is Huawei and get over 2Mbps extra, it is stable and has be continually connected for months unless I run a power cycle, or as happened recently DLM introduced interleaving again.
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