You are willing to name such blatant heretics in your support?
8. CERINTHIANS from Cerinthus and also Merinthians from Merinthus, saying that the world was created by angels, and that it is proper to be circumcised carnally, and to observe the other precepts of the law of this kind; that Jesus was only a man, and did not rise again, but asserting he will rise again. Also they gossip of a thousand future years after the resurrection in a terrestrial kingdom of Christ, according to carnal things of the belly and the delights of pleasure, wherefore they are also called Chiliasts.9. NAZOREANS, although they confess that the Son of God is the Christ, also however observe the old law, which Christians by apostolic tradition do not observe carnally, but know to understand spiritually. (St. Augustine, De Haeresibus)
Hypsistari - only reference I can find is your source.
Vadois were French Protestants.
The essential characteristic of the Catharist faith was Dualism, i.e. the belief in a good and an evil principle, of whom the former created the invisible and spiritual universe, while the latter was the author of the material world.
Toulousians - there is no reliable source which refers to them, so far as I can find.
The Albigenses asserted the co-existence of two mutually opposed principles, one good, the other evil. The former is the creator of the spiritual, the latter of the material world. ... The dualism of the Albigenses was also the basis of their moral teaching. Man, they taught, is a living contradiction. Hence, the liberation of the soul from its captivity in the body is the true end of our being. To attain this, suicide is commendable; it was customary among them in the form of the endura (starvation). The extinction of bodily life on the largest scale consistent with human existence is also a perfect aim. As generation propagates the slavery of the soul to the body, perpetual chastity should be practiced. Matrimonial intercourse is unlawful; concubinage, being of a less permanent nature, is preferable to marriage.
Peter of Bruys admitted the doctrinal authority of the Gospels in their literal interpretation; the other New Testament writings he probably considered valueless, as of doubtful apostolic origin. To the New Testament epistles he assigned only a subordinate place as not coming from Jesus Christ Himself. He rejected the Old Testament as well as the authority of the Fathers and of the Church.
Occupying a distinct place of their own were the pantheistic coteries of dissenters, the Amaurians and Ortlibenses, and perhaps other groups, like the Passagians and Speronistae, of which we know scarcely more than the names. ... The Passagii, or Passageni, a sect whose name is first mentioned in the acts of the synod of Verona, seem to have been unique in that they required the literal observance of the Mosaic law, including the Jewish Sabbath and circumcision. It is possible they are identical with the Circumcisi spoken of in the code of Frederick II. As late as 1267 and 1274 papal bulls call for the punishment of heretics who had gone back to Jewish rites, and the Passagii1037 may be referred to.
In their earliest period the Waldenses were not heretics, although the charge was made against them that they claimed to be "the only imitators of Christ." Closely as they and the Cathari were associated geographically and by the acts of councils, papal decrees, and in literary refutations of heresy, the Waldenses differ radically from the Cathari. They never adopted Manichaean elements. Nor did they repudiate the sacramental system of the established Church and invent strange rites of their own. They were also far removed from mysticism and have no connection with the German mystics as some of the other sectaries had. They were likewise not Protestants, for we seek in vain among them for a statement of the doctrine of justification by faith. It is possible, they held to the universal priesthood of believers. According to de Bourbon and others, they declared all good men to be priests. They placed the stress upon following the practice of the Apostles and obeying the teachings of the Sermon on the Mount, and they did not know the definition which Luther put on the word "justification." They approached more closely to an opinion now current among Protestants when they said, righteousness is found only in good men and good women.
They do not seem to have been sabbath keepers.
So basically you have a bunch of heretics; the only ones who kept the Sabbath also were implicated in other heretical practices, like circumcision.
The Ethiopian Orthodox Church exists today and it observes Sunday, and always has.
The Armenian Catholics are also, of course, perfectly orthodox on the question, as are the Armenian Orthodox.
We have previously noted the Nestorian Christians, considered by many as heretics, were observers of the seventh-day Sabbath.
If that was part of Nestorianism, it would have been condemned or brought up at the Council of Ephesus.
Your anonymous "missionary" is not credible:
You asked for one reference to anyone who kept the 7th day sabbath from 800 to 1500. I supplied several references from several volumes of church history by several authors. How you want to characterize the different groups doesn't really concern me.