The following explanation is based on my understanding of how the Denafrips DACs work from reading their documentation and other postings. I could be wrong in my understanding of the issue.
The Denafrips DACs use an internal reclocker when the DAC is connected using SPDIF or AES, which uses a small FIFO to buffer the PCM samples before they are clocked out using the internal clock to the R2R DAC.
SPDIF (and AES/EBU) assume that the source controls the clock, but as we all know this can introduce jitter resulting in poor performance. By buffering the data and reclocking it, the DAC can all but eliminate the issues with jitter, but this only works well if the source clock is close enough in frequency to the DACs reference clock such that the FIFO can handle the timing differences for the duration of the stream.
If the source clock is operating at a significantly different frequency from DAC clock, or the time between resetting the buffer is too long, the FIFO will either overflow or run out of samples and you'll get a drop out or stutter.
The iPurifier is doing essentially the same thing, but it probably has a deeper buffer than the Denafrips DAC, and/or is smarter about how it uses its buffer. It also likely has a better clock than the Node 2i (or at least is matched better to the DACs internal clock) so the DAC is not having the same issue buffering the data in its internal reclocker.
There may be ways to improve the problem in the DAC's firmware by being smarter about how the FIFO is used (starting the reclocking sooner or later depending on whether the source clock is faster or slower than the DACs reference clock), or perhaps there is a way to increase the FIFO size (if it's implemented in RAM) if the clocks are significantly off.
Assuming this is the issue, this problem will not occur when connecting the DAC over USB since the DAC is in control of the timing in this case instead of the source.
But I also think in @snafujg's case, it's more likely an internet/Tidal issue since he didn't have problems streaming local content and the internet has seen significantly increased streaming demand over the past several weeks due to so many people sheltering at home.