Some thoughts. First, you are concerned about your students' learning and also about your teaching. As mentioned in several comments this is clearly a positive thing and certainly not universal, if even at all common.
You ask to what extent students' feedback is credible. Student feedback clearly matters to you. Of course, sometimes student feedback is not the best evaluation of the courses they have been on. But an important question for you is this: would you prefer it if your students had these feelings or opinions about their learning experience and you knew nothing about it? Given the kind of teacher you appear to be, I think you might consider that a worse scenario.
A preliminary observation is that it seems that you might have been getting better feedback in previous years. You say that you have taught this material a few times. It seems that this year, after teaching went online, might be the first time that your feedback wasn't what you expected.
One question that might be useful is how your students' experience of your teaching has changed this year. There might be something different that you are doing now your lectures are online that you weren't doing before. It is more difficult to sense students' reactions when they aren't there live in front of you. Something very small that you are doing might be making all the difference in the wrong direction and also might be very easy to resolve, drastically improving students' experience.
One possibility (entirely speculatively) is that your lectures are less like lectures now. I mention this because you talk about extra videos that you've recorded, and it seems as though you might have changed your lectures somewhat due to their being online. One thought here is that many students joined up in the hope of actually attending lectures and seeing their lecturers face to face. In stark contrast with what they might normally appreciate, lectures that look and smell like lectures may make them feel more secure, and more as if they are receiving what they signed up for (in education-speak, they may have more 'face validity'). In a situation where students who are relying heavily on the internet can get, for example, a lot of quite good free video material online, some straight lectures directly from their lecturers might, in this new context, be novel and valued.
There are several answers here which rightly reassure you that student feedback can be both fickle and misguided. There are also answers that encourage you to mix the material up between you and your colleague. There are also, lastly, useful ideas about how to get more useful feedback from students. The latter are especially helpful. I would certainly take all of this on board. However, even if your students are fickle or misguided, I suspect that you would prefer to take that as a challenge, not as a fait accompli. My best advice would be to not take feedback too much to heart, but to keep adapting, reflecting and experimenting with your teaching styles and material and also to consider the changing needs of your groups of students and the contexts they find themselves in. It is difficult to do the latter if you never elicit any feedback from them.
I have no doubt you will get to where to want with your teaching and your students' learning. But I doubt that would be possible without feedback from your students (especially now that we don't get immediate low level feedback just from being in the same room as them).
One ancillary point. It's been suggested that students enjoy easy or merely entertaining lectures. As a director of studies, a teacher and a student counsellor I have found this to be completely untrue. Students greatly appreciate both cognitive challenge and real learning (and loathe being patronised by funny or sensational teachers who don't enable their learning). Of course, students cannot be cognitively challenged if they are completely lost or unable to understand the material at hand. It is always worth considering how to make ones teaching more engaging. Engaging teaching never prevented anybody from learning. Just ask Feynman.