You mean at the words of consecration by an validly ordained Catholic priest (only) unleavened (only) wheat bread (only) and fermented wine (only) from the juice of grapes (only) cease to exist, having become the "true body" and blood of Christ, "being corporeally present whole and entire in His physical 'reality'” in each and every particle down to the smallest visible (emphasis on visible) one. Consequently,eating and drinking are to be understood of the actual partaking of Christ in person, hence literally” though via "a supernatural mode of existence."
Until that it, the non-existent bread or wine respectively, manifests (emphasis on visibility) decay/corruption, at which point the Eucharistic christ also ceases to exist under that form, thus nothing exists.
Sources and more in refutation , by the grace of God.
My, My, how very sad that Christians must be in conflict with each other when all of this is not much more than a political/historical issue created by men and not God. Get out of your church buildings and start inviting non-believers to know Christ. Build your churches, not in brick and mortar, but in sharing Christian acts. Become fishers of men before this nation collapses in its sin. As a protestant, I lived for twenty years in a region with only catholic churches. I took communion more than twice a week as some of you would judge, illegitimately, but my focus was on a personal relationship with Jesus Christ, not the host or the wine, not the liturgy or the trappings of the church. It worked for me and if it polluted the church, they never knew it.