Cannot impute array elements

...
rg37 = hl.get_reference('GRCh37') 
rg38 = hl.get_reference('GRCh38')
rg37.add_liftover('/somepath/grch37_to_grch38.over.chain.gz', rg38) 
temp['chr'] = temp['chr'].apply(lambda x: str(int(x)) if pd.notna(x) else np.nan)
temp['location'] = temp['location'].apply(lambda x: int(x) if pd.notna(x) else np.nan)
valid_rows = temp.dropna(subset=['chr', 'location']).copy()
if not valid_rows.empty:
    try:
        ht = hl.Table.from_pandas(valid_rows)
        print("Loading complete")

        print("Sample data:", ht.show(5))

        def safe_locus(chr_val, loc_val):
            try:
                return hl.locus(hl.str(chr_val), hl.int(loc_val), reference_genome='GRCh37')
            except Exception as e:
                print(f"Error at chr: {chr_val}, location: {loc_val}")
                raise e  

        ht = ht.annotate(locus=safe_locus(ht.chr, ht.location))
        print("19 locus form transition complete")

        ht = ht.annotate(new_locus=hl.liftover(ht.locus, 'GRCh38'))
        print("37 locus form transition complete")

        ht = ht.filter(hl.is_defined(ht.new_locus))

        ht = ht.annotate(
            chr_38=ht.new_locus.contig,
            location_38=ht.new_locus.position
        )

        result_df = ht.to_pandas()

        result_df['chr_38'] = result_df['chr_38'].astype(str)
        result_df['location_38'] = result_df['location_38'].astype(float)

    except Exception as e:
        print("Error during processing:", e)

I am getting an error “cannot impute array elements”. As “Loading complete” is not printing, I believe the step “ht = hl.Table.from_pandas(valid_rows)” is not being completed.
valid_rows consist of 3 million rows.

When I tried with sample data where valid_rows consist of 5 rows, the code ran successfully and I obtained hg38 locus and there was no error. What are the things I need to further look into?