Solar Module causing frequent resets of Raspberry Pi 3B+

Hi all, I purchased the Solar Power Manager 5V 1.1 module (DFR0559) hoping to use it for a solar powered robot project however I'm finding that it's causing frequent but unpredictable/inconsistent resets of my Raspberry Pi 3B+.  Sometimes the system fails to boot while my voltmeter shows a very low voltage coming out of the power module of ~3V (and also a strange humming sound from the RPi), other times shortly after booting if I run some command like dmesg a couple of times the system just “hard” resets and my ssh session freezes. Nothing seems obviously wrong like a super high current surge or voltage fluctuations outside of tolerance (voltmeter shows values in the ranges of 5.04-5.1V @ 400-800mA).  I can confirm that with my simple off-the-shelf USB power banks the RPi can be powered on indefinitely and without these problems at all.  My test set-up is as follows:

Battery (3400mAh, 3.7V): https://www.amazon.com/dp/B08H1NZLY7?psc=1&ref=ppx_yo2ov_dt_b_product_details

Solar Panel (6W, 5V): https://www.amazon.com/dp/B09JFYPDNC?psc=1&ref=ppx_yo2ov_dt_b_product_details

External power from 5V @ 1A USB from my PC

I've tried a variety of configurations to debug the issue and can confirm that the random reboots / startup issues occur even with only the battery connected (no solar panel, no USB power from the PC).  I was unable to confirm whether they agree while solar powered due to poor weather in my area right now.

I know that the RPi can draw more than the 900mA current the module is rated for, however I did extensive testing before purchase to confirm my project does not have current demands that high, even at its peak of ~800mA.  I understand this still could theoretically be a problem if there is a spike that I can't detect/catch, though I'm unsure how to even go about diagnosing that.

Is there anything more I can do to try to diagnose what might be going on?  Thanks in advance!