Was there a Roman city in the Plain of Sarajevo?

Probably not, or to be more precise, let's just say that the evidence doesn't support the idea at present.

Firstly, if there were a large city in the area I would expect to see references to it in other sources. Apart from the Peutinger Map (of which more below), it is hard to find any references to the settlement of Ad Matricem. This would be surprising if Ad Matricem were, in fact, a large and significant town or city.

Secondly, the nineteenth century archaeologists and antiquaries would often follow Roman itineraries, and documents like the Peutinger Map, hunting for the sites they mentioned. However, without large-scale detailed excavations their identification of these places was often sketchy at best.

One of the sources you identified, Arthur Evans' Antiquarian Researches in Illyricum, is available as a downloadable PDF file from archive.com. The third section mentions Ad Matricem. It is notable that he does not mention any large-scale excavations, and that many of his identifications are, at most, only speculative.

More recent scholarship has also attempted to identify places along the routes shown on the Peutinger map. For example, the paper West Balken Roads and Settlements on Peutinger's map by Mirko Grčić of the University of Belgrade examines the Road from Salona to Sirmium, and identifies places marked on the map as follows:

... Tillurio (Trilj on Cetina river, south from Sinj), Ad Libros (Vidoši or Zidine village near Buško Blato, southeast from Duvno), In Monte Bulsineo (on Tušnica Mt. west from Duvno), Bistue Vetus (Varvara village west from Prozor or Otinovci near Kupres), Ad Matricem (Gornji Vakuf, possibly Travnik), Bistua Nuova (Vitez village on Lašva river), Stanecli (Kiseljak spa near Sarajevo).

• Mirko Grčić, 2017, (my emphasis)

So the location of Ad Matricem, whatever type of settlement it eventually turns out to be, remains uncertain.

Unfortunately, no archaeological investigations carried out in the Plain of Sarajevo to date have identified the remains of a large, walled Roman city with towers (which is what might be suggested by the symbol used by the 13th century scribe on the Peutinger Map). Roman walls, in particular, are very distinctive in their construction and are usually easily identified, even when later Medieval walls are built on top of them.

Unfortunately, the symbol used for Ad Matricem doesn't appear anywhere else on the map, so we can't be certain what it was intended to represent. It might have been a city or a town (the Romans used a number of terms to describe different types of settlement that we would just call "a town"). It could have been something else entirely (perhaps military in nature), or even just a later scribal error (of which there are many on the map!). The walls & tower suggest a settlement, so if it wasn't simply a scribal error (or a scribal addition for other reasons - see below), I'd say it was "probably a town", but I wouldn't make any assumptions about its size based solely on the map.

The Peutinger Map

So we come to the Peutinger Map itself. This is often described as:

"... a 13th-century parchment copy of a possible Roman original".

as in the Wikipedia article, cited above. However, modern scholarship suggests that it probably wasn't a "copy", in the modern sense of the word, but rather a re-construction, based on a number of earlier sources. It is unique, and that makes it problematic. To quote Benet Salway's paper The Nature and Genesis of the Peutinger Map, the Peutinger Map is:

... without precedent in Roman cartography or impact on later medieval cartography, the mapping of itinerary data onto a base map of the oecumene is likely to be a genuine innovation of the designer of the archetype.

As such, it should be used with caution, even though

... on the assumption that it represents a Roman original, the Peutinger map has for a long time had a special significance as the sole surviving witness to the character of ancient Roman, and in particular Latin, mapping of the entire known world

• Salway (2005)

The truth is that we don't know why it was made, what sources were consulted, or who it was made for, although we may be getting closer to establishing where it was made and when.

Salway also addresses the question of Ad Matricem:

" ... the treatment of Ad Matricem (5A5), an otherwise unknown and unremarkable location, in the upper Vrbas valley of Bosnia. This is the one place on the entire map that is highlighted by its symbol in a way completely out of proportion to its political, geographical and cultural significance in Roman history. The place is marked by a unique three-turreted symbol that seems to stand somewhere between the individuality of the walled town vignettes and the uniformity of the standard signs for cities, spas and other places (Fig. 2). It is hard to see why this locality in Dalmatia, 90 kilometres inland from Salonae, should merit such prominence other than because of some personal connection with either the original designer or subsequent redactor of the Peutinger map".

• Ibid

So that may be the solution to the apparent paradox. Why does the map show a unique symbol for a place which doesn't appear to have left correspondingly large archaeological remains? The scribe, or someone else associated with the production of the Peutinger map, may simply have had a personal connection to the area.

Clearly, if the symbol was really, shall we say "artistic licence" (as suggested above), then the size of the settlement also comes into question. If Ad Matricem is, in fact, a much smaller settlement, then its remains may be under one of the modern sites suggested by Mirko Grčić. However, unless an inscription of some sort bearing the name of the place is found, its location is likely to remain a matter of speculation.