Attach a SAVE GAME (.aoe2spgame) or GAME RECORDING (.aoe2record) of the match where you encountered the issue. Link it below if using an external file service.
recorings were this bug happens cannot be watched/ it gets out of synch when the bug would occur
A similar bug is that you can place gates on enemy walls, and the enemy walls get deleted.
The walls must be out of your LOS though (you need to scout them, and then walk away from them).
I can confirm that I experienced the same bug. And it is not only related to new civ because my enemy did it with Turks. I cannot see what building did he use because as the author of the post says, the replay goes out of sync.
Attach a SAVE GAME (.aoe2spgame) or GAME RECORDING (.aoe2record) of the match where you encountered the issue. Link it below if using an external file service.
In this case the enemy was using Turks so I am almost sure this bug occurs also with Towers or other type of buildings. And it is different from the “Gate delete walls” bug because here he did not even needed to build it but simply placing the foundation was enough.
These details are CRITICAL; DO NOT skip them or your issue may not be reviewed.
GAME BUILD #: 101.101.44725.0 6115729
GAME PLATFORM: Steam
OPERATING SYSTEM: Windows 10
ISSUE EXPERIENCED
*Ranked arena game, trying the new Sicilians (Hoping them to be my new favourite civ) making a couple of donjons to guard relics, failing to keep them up, no worries, I’m just trying them out. All of a suddend I see a massive 4 tiles hole in my arena walls that was not there and enemy scouts running ine (like 12 of them) I give fault to my ADD at first, thinking I might have selected the walls and deleted them without noticing, stupid me. I spend 15 minutes chasing scouts around and plugging the whole. After wich… Another Hole appears and knights come in, now I know the opponent might be using some bug I don’t know about, I ask about it, the “gentleman” doesn’t reply, I resign…
I attach a replay file *
FREQUENCY OF ISSUE
How often does the issue occur? CHOSE ONE; DELETE THE REST!
Less than 25% of the time / matches I play (RARELY)
REPRODUCTION STEPS
List CLEAR and DETAILED STEPS we can take to reproduce the issue ourselves… Be descriptive!
Here’s the steps to reproduce the issue:
Have the Lords of the West DLC
Play a ranked map as Sicilians
Get arena chosen as a map
EXPECTED RESULT
What was SUPPOSED to happen if the bug you encountered were not present?
My walls should have been there…
IMAGE
A replay file is worth a thousand (technically way more) images
It was a bad day for me, and I had waited a lot to try the new DLC and I hadn’t played in almost 2 months… needless to say this was really not amusing, and I’m trying to be civil here…
*
This is an exploit which came up with the removal of the building scan exploit (I assume). You can remove the enemy walls by placing building foundations…how this stuff got past testing is beyond me.
Thank you for the reports! Just dropping in to note that this issue has been identified by the team and a fix should be showing up in today’s hotfix.
GAME INFORMATION
These details are CRITICAL; DO NOT skip them or your issue may not be reviewed.
Seems like a pretty bad bug 
I sense (hope) a hotfix soon, if this bug is fully confirmed