Yes, what you’re experiencing is exactly what is realistically to be expected. I described things more in depth previously as well as a good way to handle catching up if needed, but the key takeaways here as it pertains to your question of whether or not it’s normal are:
SRS is genuinely an incredible tool for retention, but it can’t magically dispense with reality. This is probably the most important thing to understand in order to maintain doing it long term.
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Unfortunately, you don’t magically stop forgetting things just because you went on vacation or had other life commitments.
The bottom line is that you first saw some items at time X and you will forget them after some given time frame Y without having encountered them again in some capacity, whether that be another review or in the wild. All activating vacation mode really does is pushes all of your reviews (including all future ones) outside of their optimal review window which means you are going to have higher miss rates on basically everything that is a large enough percentage deviation from the time frame in which you naturally forget an item without further review. It affects items that are already on longer intervals much less because the overall percentage those days you missed are of the overall time frame is small, but it still affects everything nonetheless.
That’s why vacation mode is realistically mostly more harmful than helpful in reality. It keeps you from having a huge number of reviews piled up which can be demotivating and if that keeps someone from quitting, then that part can be a positive, but, that comes at the expense of actively screwing with the SRS intervals for everything you’ve already done in a negative way.