/z/ + /ð/ = /zdð/?

I was wondering what exactly happens when the common English speaker* pronounces /z/ and /ð/ right after, for example , the word - combo "is this ...".
Honestly, for me it's almost impossible to pronounce this combination without making a very small break between the /z/ and the /ð/.

When I hear Americans pronounce this combo, usually hear something like /zdð/ or some sound which comes out in between the /d/ sounds and the /ð/, (as a very soft d, if I try to describe it in words).

I'm pretty sure about what I hear, and I was wondering if someone can verify what I'm hearing and maybe elaborate on the subject.

*As usual, I'm mostly interested in american pronunciation, with a bias toward general american, or at least midwestern accent.

Edit: here are some examples: (wait a second or two for the "is this" combo)
https://youtu.be/w4RLfVxTGH4?t=226
https://youtu.be/7LPJrzZaoZg?t=148
https://youtu.be/UpBycmR3_lQ?t=77
https://youtu.be/LlEhlw_d5N8?t=285
https://youtu.be/h6Dk3RgNOKI?t=902
https://youtu.be/td7Dcsco-WY?t=1688

I haven't found any sources that indicate something special about this particular environment. A stop-like realization of /ð/ as something like [d̪] or [d̪ð] is a common allophone in a number of accents, but it seems to be conditioned more strongly when /ð/ is preceded by a plosive (this can be seen as a kind of assimilation) or when it is utterance-initial/preceded by silence than when it is preceded by a fricative (like /z/). Stop-like realizations of /ð/ are supposed to be more common after fricatives and affricates than after vowels or liquids, however.

• "Applied English Phonology", by Mehmet Yavas, says that word-initial /ð/ may be assimilated to a preceding alveolar plosive in manner of articulation, and may possibly be completely assimilated/assimilated in place of articulation to a preceding /s/ or /z/:

  unstressed initial /ð/ in words such as the, this, that becomes assimilated (with or without complete assimilation) to previous alveolar consonants (e.g. what the heck [wɑt̪d̪əhɛk], run the course [ɹ̣ʌnːəkɔɹ̣s], till they see [tɪlːesi], how's the dog? [haʊzːədɔg], takes them [teksːəm]) (p. 67)

• "The stop-like modification of /ð/: A case study in the analysis and handling of speech variation", by Sherry Y. Zhao (2007) seems relevant. I confess I haven't finished reading through it, but the abstract says

  It is found that stop-like /ð/ occurs most often when it is preceded by silence or when preceded by a stop consonant. The occurrence is less frequent when /ð/ is preceded by a fricative or an affricate consonant. This modification rarely occurs when /ð/ is preceded by a vowel or liquid consonant.

  Table 4.6 (p. 46) indicates that in the AEMT recordings that Zhao looked at, stop-like realizations of /ð/ after /z/ occured only 25% of the time (13 out of 52 tokens), which is actually a lower proportion than for /ð/ after /v/, which had a stop-like realization 30% of the time (67 out of 223 tokens), and lower than the proportions for /ð/ after any of the plosives (/p/, /t/, /k/ or /d/).

I haven't analyzed the phonetics of your examples, but I think I hear friction in /ð/ in at least the second and third ones. The first one is too quick for me to hear clearly whether the sound is fricative or stop-like.