Several entries have the resolution value set to 99 when obtained from PDB and 0 when obtained from mmCif.

Each was cryo-EM with resolutions in the range 3.35 - 3.8 Å.

4 examples are
(3j8h, 3jaj (available only in mmCIF).
6hu9, 7o3e (available as PDB files).

By experimenting, I found that

• The PDB entries have the resolution reported in REMAK 2 (not parsed at all) and in REMARK 3 (using a format not recognized by the PDBFileParser). --> they are left as the default resolution value (99).
• The mmCif entries have the . value in the _refine.ls_d_res_high field, which indicates that the value may be used to identify that there is no appropriate value for the item or that a value has been intentionally omitted (I don't know why omitted) --> when the period (.) is parsed into float, it is wrongly parsed as (0.0)