Letter disappears mysteriously: م (mim)
I've noticed the following repeating pattern: when م (mim) follows ل (lam), it is not rendered, for example in the words اَلْمَدينة and اَلْمُحامي.
This seems to be true only for certain typefaces. Chrome on Mac chooses Geeza Pro to render Arabic. When I play around with other typefaces in a text editor, I see that Arial and Times New Roman do render م, but other typefaces don't (like Al Bayan, Al Nile, Al Tarikh, Baghdad, Geeza Pro). Firefox/Mac renders the word well, as it seems to use a different typeface (din-round or Arial).
Is this an error or is this intentional (a stylistic difference)??
P.S. I also noticed some other words get very difficult to read, such as اَلْأُسْتاذ.
Those are ligatures. The combination of Lam + Alif is the most known, but there are many more of those combination characters. Some fonts use more of those ligatures than other fonts. For example the font used by dictionary https://www.almaany.com/ uses them a lot.
This pdf gives an overview. Lam + Meem is character FCCC.
Wow, I see the difference now! Thanks for the explanation, I wouldn't have spotted it by myself. Even if it's explained on wikipedia (https://en.wikipedia.org/wiki/Arabic_alphabet#Ligatures).