The Evasive Ether: Existence of diethynyl ether?
You can find a nice discussion of diethynyl ether and some of its derivatives here:

Ooi, I. H., &amp; Smithers, R. H. (1989). Bis [(trimethylsilyl) ethynyl] ether: a moderately stable C4H2O derivative. The Journal of Organic Chemistry, 54(6), 1479-1480.

https://pubs.acs.org/doi/pdf/10.1021/jo00267a053

They write that "little or nothing is known about diethynyl ether", and they were only able to find theoretical (INDO) calculations in their literature search about the compound, as opposed to actual reports of its synthesis. They do mention that the following authors managed to synthesize a dimethyl derivative, $\ce{Me-C#C-O-C#C-Me}$, but reported that it explodes at room temperature (and I infer, from what Ooi and Smithers wrote, that diethynyl ether would be even more unstable):

Brandsma, L., &amp; Arens, J. F. (1962). Chemistry of acetylenic ethers LVI Di‐(alk‐1‐ynyl) ethers and thioethers. Recueil des Travaux Chimiques des Pays‐Bas, 81(6), 510-516.

https://onlinelibrary.wiley.com/doi/abs/10.1002/recl.19620810610

They themselves (Ooi and Smithers) were able to synthesize a di-trimethylsilyl derivative, $\ce{Me_3Si-C#C-O-C#C-SiMe_3}$ which, while stable when dissolved in $\ce{CH_2Cl_2}$ and stored in a freezer, degrades overnight when stored neat at room temperature.

In summary, for $\ce{R-C#C-O-C#C-R}$, larger R's provide added stability:

R = H (diethynyl ether): If it were ever synthesized, it would probably have a very short half-life, except under specalized conditions.

R = Me: Has been synthesized, but explodes at room temperature

R = $\ce{Me_3Si}$: Low to moderate stability, as described above.   Ooi and Smithers write that the added  stability provided by the trimethylsilyl groups "is probably both steric and electronic." 

See also:

Arens, J. F. (1960). Ethynyl ethers and thioethers as synthetic intermediates. Advances in organic chemistry, 2, 117.