Although the De Passione Domini is a fairly short hexameter poem (80 lines), it contains a rather high frequency of elisions. Out of the poem's 80 lines, 42 of them (by my count) contain at least one elision. There are 6 lines with 2 elisions (6, 11, 36, 37, 40, 48), and 3 lines with 3 elisions (21, 35, 57), for a grand total of 53 in the poem. Here are the 3 lines with 3 elisions:
21: Pauperiem extremam et rerum inferiora secutus
35: Fige animo et testes et caeci infanda Pilati
57: Disce adversa pati et propriae invigilare saluti
For a slightly different configuration, see Manitius, Geschichte der Christlich-Lateinischen Poesie p. 49 n. 4. A couple of these differences are due to our using different texts to calculate. For example, one of his 3 lines with 3 elisions is 56, which is line 57 in the CSEL version of the text. Again, he lists line 3 as having two elisions, whereas I have it as having one. The CSEL text reads
Respice me, me conde animo, me pectore serva.
The app. crit., on the other hand, shows a variant of in pectore instead of pectore, which would generate another elision.
One difference, though, that I can't figure out based on the app. crit. is line 48. I have this as a two-elision line, whereas Manitius does not list it among his two-elision lines:
Atque ingens lateris vulnus, cerne inde fluorem.The only variant listed by the CSEL's app. crit. is lateri for lateris, but this doesn't effect the elisions.