There is only one time during the year that God commanded the people to eat Unleavened Bread.  It began at Passover, Abib/Nisan 14,  through to the last day of the 7day feast of Unleavened Bread.
 
Lev. 23:5 In the 14th day of the first month at even is the Lord's Passover.
 
"At even" means when one day changes over to the next, which is when the first three evening stars appear. It is not the 13th anymore, but is the beginning of the new day, the 14th.
 
In the evening of the 13th after the day changed over to the 14th, was Passover the day of preparation.  That evening Jesus had the last supper. This was the night he was betrayed.
 
He knew he would be crucified on this day at the same time the lambs were being killed in the following afternoon, yet still on the 14th. He was the Passover Lamb of God  and must die on this day to fulfill this feast.  But can we say they ate unleavened bread?  Very definitely yes!
 
1 Cor 11:23-29  For I have received of the Lord that which also I  deliver unto you, That the Lord Jesus the same night in which he was betrayed took bread. And when he had given thanks, he brake it, and said, Take eat;  this is my body, which was broken for you: this do in remembrance of me. After the same manner he also took the cup, when he had supped, saying, This cup is the New Testament in my blood: For as often as ye eat this bread, and drink this cup, ye do show the Lord's death till he come.
 
Exod. 34:25  Thou shalt not offer  the blood of my sacrifice with leaven;  neither shall the sacrifice of the feast of Passover be left unto the morning.
 
The wine symbolizes his blood, and the bread is symbolic of his body.  Leaven symbolizes SIN.   The unleavened bread is symbolic of his SINLESS state.  He had to be sinless in order to be the sacrificial Lamb of God.
 
The sacrificial lambs had to be perfect in every way in order for their blood to be sprinkled  on the mercy seat in the temple to atone for the sins of the people.  These lambs were a representation of Jesus, our perfect sacrificial Lamb, who would go into the holy of holies and sprinkle his perfectly sinless blood onto the mercy seat in the heavenly tabernacle for our sins.
 
Pilate found no fault in Jesus when he examined him.  God found no fault in him as he stated more than once: This is my beloved Son, in whom I am well pleased."
 
When we eat leavened bread, we are proclaiming that Jesus had sin in him.  If he did, he could not have offered his  blood on the heavenly
mercy seat for our sins, therefore NO MERCY AND NO  SALVATION for anyone on this planet.  Why could not the remains of the Passover lamb be left unto the morning (the dawning of the 15th at even).  Because that is the first day of the feast of Unleavened Bread, which is a High Sabbath, a holy day of worship. They were not allowed to do anything nor handle the dead on  a weekly Sabbath,  or a high Sabbath.
 
Unleavened Bread:
 
Lev. 23:6, 7, 8,  And on the 15th day of the same month  is the feast of unleavened bread unto the Lord: seven days ye must eat unleavened bread. In the first day  ye shall have a holy convocation: ye shall do no servile work therein. In the seventh day is a holy convocation.
 
So from Passover, the 14th, through the seven days of unleavened bread,  God commanded they eat only  unleavened bread.   This should not be such a mystery as the scriptures do clear this up very plainly.  Were  there  consequences for disobedience? Yes!  This is especially a dangerous error.  If we do not recognize his sinless state, we are reading or listening to, or teaching the Word unworthily.  Then we are found guilty of his blood and body.
 
Hebrews 10:29  Of how much sorer punishment, suppose ye, shall he be thought worthy, who hath  trodden under foot the Son of God, and hath counted the blood of the covenant, wherewith he was sanctified, an unholy thing, and hath done despite unto the Spirit of grace.
 
Doing despite unto the Holy Ghost is a very serious error.
 
Matt. 12:31 Wherefore I say unto you,  All manner of sin and blasphemy shall be forgiven unto men: but the blasphemy against the Holy Ghost shall not be forgiven unto men.
 
Very serious business indeed.  One needs to be so careful when teaching or giving their opinion on this subject, lest they lead others into gross error.
 
God bless