Too many DEGs?

Hi,

I am a fresh user of glmGamPoi and thanks for providing this awesome tool! I tried to identify DEGs in scRNA and successfully run the following code:
```
load('/Volumes/kfsd/GSE200903_new_combined_cluster_FibroSamples_2022-01-14.RData')
combine_cluster <- as.SingleCellExperiment(combined_cluster)

set.seed(1)
colData(combine_cluster)
# Take highly expressed genes and proper cells:
combine_cluster_subset <- combine_cluster[rowSums(counts(combine_cluster)) > 100,
which( ! is.na(combine_cluster$CellType) & combine_cluster$CellType
%in% c("fibroblasts"))]

# add a stim2 based on stim
colData(combine_cluster_subset)$stim2 <- colsplit(colData(combine_cluster_subset)$stim,
split = "_", names = c('cell', 'trt','time'))$trt
# Convert counts to dense matrix
counts(combine_cluster_subset) <- as.matrix(counts(combine_cluster_subset))
# Remove empty levels because glm_gp() will complain otherwise
colData(combine_cluster_subset)$stim2 <- as.factor(colData(combine_cluster_subset)$stim2)
colData(combine_cluster_subset)$stim2 <- relevel(colData(combine_cluster_subset)$stim2, ref = "normal")

fit <- glm_gp(combine_cluster_subset, design = ~ stim2 ,
reference_level = "normal")
summary(fit)
colnames(fit$Beta)

# The contrast argument specifies what we want to compare
# We test the expression difference of stimulated and control T-cells
#
# There is no sample label in the colData, so we create it on the fly
# from `stim` and `ind` columns in colData(fit$data).
de_res <- test_de(fit, contrast = `stim2PDAC`,
pseudobulk_by = paste0(stim2, "-", rownames(colData(combine_cluster_subset))))

# The large `lfc` values come from groups were nearly all counts are 0
# Setting them to Inf makes the plots look nicer
de_res$lfc <- ifelse(abs(de_res$lfc) > 20, sign(de_res$lfc) * Inf, de_res$lfc)

# Most different genes
de_res<-de_res[order(de_res$pval), ]
```
However, I identified 11752 DEGs out of 14537 genes and I found many genes has df1=1.
```
head(de_res)
name pval adj_pval f_statistic df1 df2 lfc
35 Rpl7 0 0 3244.666 1 20005.31 -0.5195890
44 Pi15 0 0 2180.603 1 20005.31 -1.6835958
124 Il1r1 0 0 3883.918 1 20005.31 2.2249821
132 Fhl2 0 0 5068.944 1 20005.31 4.8176423
158 Gls 0 0 1635.089 1 20005.31 0.9511179
164 1700019D03Rik 0 0 3380.809 1 20005.31 -2.7193859
```

I wondered how could I address this problem? Thanks in advance!

Best,
Kun