wow !!! the upload speed is 13.58 times better than the download speed.
That's not surprising. We see that phenomenon frequently in everyday life. If for example a Taylor Swift concert ends at the National Stadium, the immediate area will have much more pedestrian outflow than inflow — much more foot traffic headed away from the National Stadium than toward it. To some extent the staff can (and presumably do) shift the barriers between outflow and inflow. However, even if the inflow lane is quite narrow it can still be much faster to traverse for the few people who may use it (staff, law enforcement, etc.)
Likewise, on a mobile network if practically everyone is streaming YouTube, Netflix, and other video content — and downloading big applications — there could be lots of congestion on the download links in a particular area. The carrier can "shift the barriers" to some extent, but the much less used upload links could be comparatively speedy.
Also, a lot of mobile devices are...well, let's just say they can make strange decisions even if the mobile network is doing a great job. The device might latch onto a subpar download link (or set of download links) while having much better upload links with the carrier's towers. As a crude method to rule out phone-specific anomalies you could try remaining stationary, power cycling the phone, then re-running the test. Or use a different phone (different make and model) at the same location to see if the results are much different. Also try 4G and 5G to see if you get any substantially different results. 4G might actually be faster at a particular location at a particular time.
That said,
OpenSignal aggregates lots of observations and rates SIMBA's network as the overall weakest in Singapore in June, 2025 (most recent month available). SIMBA's download speeds are (on average) substantially lower than those of other networks, and so are upload speeds. As this single speed test suggests, the gap between download speeds is bigger than it is for upload speeds — SIMBA is less comparatively weak on the upload side. SIMBA is quite inexpensive, though (especially on the $5 senior plan), and that factor alone counts for a lot. And SIMBA doesn't prioritize network access the way M1, StarHub, and Singtel do with respect to the various MVNOs since SIMBA doesn't have any MVNOs.