telco, i'm using celcom and digi, both sim1 and sim2.

first notice it when get out from airplane, couldn't get any signal after 2 hours. end up taking normal taxi rather than grab.

second time is when came out from a coldroom, the signal took 1+ hours to recover back.

since then i've been very cautious about this matter, always keep an eye. turns out signal is not stable too...