I read your review -- I didn't think you were being overly harsh - you clearly described the issue, provided evidence of the issue, and proposed a remedy (recall). The remedy might be a little extreme, but I believe Siglent should, at least, offer to repair the affected scopes under warranty. The repaired scopes would, of course, have a valid warranty for the remainder of the warranty period, and be correctly calibrated before shipping back to customers. Siglent should at least pay for shipping 1 way. If they want to be seen as a class act, they should pay for shipping both ways.
Ignoring the issue, hoping it will die out, or providing the caps and asking users to fix it (risking damage not covered under warranty) are, in my opinion, all signs of a company that does not stand behind its products, and does not care about its customers.
I sympathize with Siglent - They have made a great product, but it has a flaw that cannot be patched with software - that is bad luck. But if you want to play the game, you have to accept losing hands as well as winning ones. Fixing this may wipe out all the profits for the affected units. Or may even cost more than that. But if Siglent wants a good reputation (and reputation for reliability and accuracy is absolutely necessary to sell test instruments), they need to put on their big-boy pants and fix this. A simple statement from Siglent would lay all this to rest;
"Siglent will promptly honor all warranty claims against defective products. Please contact Siglent with the model number & serial number of the affected unit, and a brief description of the problem. Siglent will provide a shipping label to affix to your box to ship it to the nearest Siglent repair facility. The device will either be repaired or replaced with an equivalent device at Siglent's option. You can expect return shipment within 10 business days of Siglent receiving the defective device."
A manufacturer or service provider should not argue the validity of a claim -- that is never a winning argument. Just fix or replace. If no satisfaction can be found, offer a refund.
How hard would that be? Apply that consistently, and you'll have loyal customers rallying to your defense every time something happens.